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Sample records for 2d electron gas

  1. Quantum Oscillations in an Interfacial 2D Electron Gas.

    Zhang, Bingop [Zhejiang Univ., Hangzhou (China); Lu, Ping [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Liu, Henan [Univ. of North Carolina, Charlotte, NC (United States); Lin, Jiao [Zhejiang Univ., Hangzhou (China); Ye, Zhenyu [Zhejiang Univ., Hangzhou (China); Jaime, Marcelo [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab); Balakirev, Fedor F. [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab); Yuan, Huiqiu [Zhejiang Univ., Hangzhou (China); Wu, Huizhen [Zhejiang Univ., Hangzhou (China); Pan, Wei [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Zhang, Yong [Univ. of North Carolina, Charlotte, NC (United States)

    2016-01-01

    Recently, it has been predicted that topological crystalline insulators (TCIs) may exist in SnTe and Pb1-xSnxTe thin films [1]. To date, most studies on TCIs were carried out either in bulk crystals or thin films, and no research activity has been explored in heterostructures. We present here the results on electronic transport properties of the 2D electron gas (2DEG) realized at the interfaces of PbTe/ CdTe (111) heterostructures. Evidence of topological state in this interfacial 2DEG was observed.

  2. Hybrid Quantum Dot-2D Electron Gas Devices for Coherent Optoelectronics

    Dettwiler, F.; Fallahi, P.; Scholz, D.; Reiger, E.; Schuh, D.; Badolato, A.; Wegscheider, W.; Zumbühl, D. M.

    2014-01-01

    We present an inverted GaAs 2D electron gas with self-assembled InAs quantum dots in close proximity, with the goal of combining quantum transport with quantum optics experiments. We have grown and characterized several wafers -- using transport, AFM and optics -- finding narrow-linewidth optical dots and high-mobility, single subband 2D gases. Despite being buried 500 nm below the surface, the dots are clearly visible on AFM scans, allowing precise localization and paving the way towards a h...

  3. Magneto-oscillations due to electron-electron interactions in the ac conductivity of a 2D electron gas

    Sedrakyan, T. A.; Raikh, M. E.

    2007-01-01

    Electron-electron interactions give rise to the correction, \\delta\\sigma^{int}(\\omega), to the ac magnetoconductivity, \\sigma(\\omega), of a clean 2D electron gas that is periodic in \\omega_c^{-1}, where \\omega_c is the cyclotron frequency. Unlike conventional harmonics of the cyclotron resonance, which are periodic with \\omega, this correction is periodic with \\omega^{3/2}. Oscillations in \\delta\\sigma^{int}(\\omega) develop at low magnetic fields, \\omega_c\\ll\\omega, when the conventional harm...

  4. Conductivity of disordered 2d binodal Dirac electron gas: Effect of the internode scattering

    Sinner, Andreas

    2016-01-01

    We study the dc conductivity of a weakly disordered 2d Dirac electron gas with two bands and two spectral nodes, employing a field theoretical version of the Kubo--Greenwood conductivity formula. In this paper we are concerned with the question how the internode scattering affects the conductivity. We use and compare two established techniques for treating the disorder scattering: The perturbation theory, there ladder and maximally crossed diagrams are summed up, and the functional integral approach. Both turn out to be entirely equivalent. For a large number of random potential configurations we have found only two different conductivity scenarios. Both scenarios appear independently of whether the disorder does or does not create the internode scattering. In particular we do not confirm the conjecture that the internode scattering tends to Anderson localization.

  5. Finite-size scaling in a 2D disordered electron gas with spectral nodes

    Sinner, Andreas; Ziegler, Klaus

    2016-08-01

    We study the DC conductivity of a weakly disordered 2D electron gas with two bands and spectral nodes, employing the field theoretical version of the Kubo–Greenwood conductivity formula. Disorder scattering is treated within the standard perturbation theory by summing up ladder and maximally crossed diagrams. The emergent gapless (diffusion) modes determine the behavior of the conductivity on large scales. We find a finite conductivity with an intermediate logarithmic finite-size scaling towards smaller conductivities but do not obtain the logarithmic divergence of the weak-localization approach. Our results agree with the experimentally observed logarithmic scaling of the conductivity in graphene with the formation of a plateau near {{e}2}/π h .

  6. The a-c response of a 2-D electron gas on liquid helium in a magnetic field

    The low-frequency a-c response of a 2-D electron gas on liquid helium in a magnetic field is analyzed in terms of ρxx and ρxy, the components of the magnetoresistivity tensor. The electrons are screened by parallel electrodes and the system forms a 2-D transmission line. The 2-D wave equation is solved numerically for a bounded electron sheet in a rectangular geometry which is excited by one of the electrodes. For ωτ xx and ρxy. The effects of these skin depths on measurements of the magnetoresistance and a-c Hall effect are demonstrated. The relationship to the dc Hall effect and to edge magnetoplasmons is shown. The effects of incomplete screening, density inhomogeneities and edge capacitance are also discussed

  7. Metal-insulator transition of 2d electron gas in a random magnetic field

    Wang, X R; Liu, D Z

    1999-01-01

    We study the metal-insulator transition of a two-dimensional electron gas in the presence of a random magnetic field from the localization property. The localization length is directly calculated using a transfer matrix technique and finite size scaling analysis. We argue that there is a metal-insulator transition in such a system and show strong numerical evidence that the system undergoes a disorder driven Kosterlitz-Thouless type metal-insulator transition. We will also discuss a mean field theory which maps the random field system into a two-dimensional XY-model. The vortex and antivortex excitations in the XY-model correspond to two different kinds of magnetic domains in the random field system.

  8. Can fractional quantum Hall effect be due to the formation of coherent wave structures in a 2D electron gas?

    Mirza, Babur M.

    2016-05-01

    A microscopic theory of integer and fractional quantum Hall effects is presented here. In quantum density wave representation of charged particles, it is shown that, in a two-dimensional electron gas coherent structures form under the low temperature and high density conditions. With a sufficiently high applied magnetic field, the combined N particle quantum density wave exhibits collective periodic oscillations. As a result the corresponding quantum Hall voltage function shows a step-wise change in multiples of the ratio h/e2. At lower temperatures further subdivisions emerge in the Hall resistance, exhibiting the fractional quantum Hall effect.

  9. Beltrami States in 2D Electron Magnetohydrodynamics

    Shivamoggi, B. K.

    2015-01-01

    In this paper, the Hamiltonian formulations along with the Poisson brackets for two-dimensional (2D) electron magnetohydrodynamics (EMHD) flows are developed. These formulations are used to deduce the Beltrami states for 2D EMHD flows. In the massless electron limit, the EMHD Beltrami states reduce to the force-free states, though there is no force-free Beltrami state in the general EMHD case.

  10. 2D microwave imaging reflectometer electronics.

    Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C

    2014-11-01

    A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program. PMID:25430247

  11. 2D microwave imaging reflectometer electronics

    Spear, A. G.; Domier, C. W., E-mail: cwdomier@ucdavis.edu; Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C. [Electrical and Computer Engineering, University of California, Davis, California 95616 (United States); Tobias, B. J. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

    2014-11-15

    A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

  12. The magnetic translation symmetry and the one-loop Dyson equation for the 2D-electron gas

    The Magnetic Translation (MT) symmetry is used for deriving a summation formula for eigenfunctions of the 2D-Schroedinger equation in a homogeneous magnetic field. The Dyson equation for the propagator is solved in the one-loop approximation when only the first Landau level is filled. The Landau level degeneracy is not broken in this approximation. (author). 7 refs

  13. 2D hydrodynamic simulations of a variable length gas target for density down-ramp injection of electrons into a laser wakefield accelerator

    Kononenko, O.; Lopes, N. C.; Cole, J. M.; Kamperidis, C.; Mangles, S. P. D.; Najmudin, Z.; Osterhoff, J.; Poder, K.; Rusby, D.; Symes, D. R.; Warwick, J.; Wood, J. C.; Palmer, C. A. J.

    2016-09-01

    In this work, two-dimensional (2D) hydrodynamic simulations of a variable length gas cell were performed using the open source fluid code OpenFOAM. The gas cell was designed to study controlled injection of electrons into a laser-driven wakefield at the Astra Gemini laser facility. The target consists of two compartments: an accelerator and an injector section connected via an aperture. A sharp transition between the peak and plateau density regions in the injector and accelerator compartments, respectively, was observed in simulations with various inlet pressures. The fluid simulations indicate that the length of the down-ramp connecting the sections depends on the aperture diameter, as does the density drop outside the entrance and the exit cones. Further studies showed, that increasing the inlet pressure leads to turbulence and strong fluctuations in density along the axial profile during target filling, and consequently, is expected to negatively impact the accelerator stability.

  14. Correlated Electron Phenomena in 2D Materials

    Lambert, Joseph G.

    In this thesis, I present experimental results on coherent electron phenomena in layered two-dimensional materials: single layer graphene and van der Waals coupled 2D TiSe2. Graphene is a two-dimensional single-atom thick sheet of carbon atoms first derived from bulk graphite by the mechanical exfoliation technique in 2004. Low-energy charge carriers in graphene behave like massless Dirac fermions, and their density can be easily tuned between electron-rich and hole-rich quasiparticles with electrostatic gating techniques. The sharp interfaces between regions of different carrier densities form barriers with selective transmission, making them behave as partially reflecting mirrors. When two of these interfaces are set at a separation distance within the phase coherence length of the carriers, they form an electronic version of a Fabry-Perot cavity. I present measurements and analysis of multiple Fabry-Perot modes in graphene with parallel electrodes spaced a few hundred nanometers apart. Transition metal dichalcogenide (TMD) TiSe2 is part of the family of materials that coined the term "materials beyond graphene". It contains van der Waals coupled trilayer stacks of Se-Ti-Se. Many TMD materials exhibit a host of interesting correlated electronic phases. In particular, TiSe2 exhibits chiral charge density waves (CDW) below TCDW ˜ 200 K. Upon doping with copper, the CDW state gets suppressed with Cu concentration, and CuxTiSe2 becomes superconducting with critical temperature of T c = 4.15 K. There is still much debate over the mechanisms governing the coexistence of the two correlated electronic phases---CDW and superconductivity. I will present some of the first conductance spectroscopy measurements of proximity coupled superconductor-CDW systems. Measurements reveal a proximity-induced critical current at the Nb-TiSe2 interfaces, suggesting pair correlations in the pure TiSe2. The results indicate that superconducting order is present concurrently with CDW in

  15. Electron transfer and ionic displacements as the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution.

    Cantoni, Claudia [ORNL; Gazquez Alabart, Jaume [ORNL; Miletto Granozio, Fabio [Universita` di Napoli “Federico II”; Oxley, Mark P [ORNL; Varela del Arco, Maria [ORNL; Lupini, Andrew R [ORNL; Pennycook, Stephen J [ORNL; Aruta, Carmela [Universita` di Napoli “Federico II”; Scotti di Uccio, Umberto [Universita` di Napoli “Federico II”; Perna, Paolo [Universita` di Napoli “Federico II”; Maccariello, Davide [Universita` di Napoli “Federico II”

    2012-01-01

    We present direct, atomic-column-resolved scanning transmission electron microscopy and electron energy loss measurements of atomic displacements and Ti valence in abrupt, conductive LAO/STO interfaces. We find that two distinct but interrelated mechanisms are responsible for screening the diverging electric potential in the LAO film: 1) charge injection in the interfacial Ti planes, and 2) dielectric relaxation in both LAO and STO through ionic displacements. The injected charge density decays over a length of nearly 3 unit cells within the STO substrate. The total injected charge is lower than predicted by pure electronic reconstruction. The origin of this discrepancy is attributed to cation and oxygen displacements, which we observe in both LAO and STO, and generate a polarization opposite to the intrinsic polarization of the LAO film. Our data attribute a minor role to oxygen vacancies and cation intermixing.

  16. Graphene as a platform to study 2D electronic transitions

    Bouchiat, Vincent; Kessler, Brian; Girit, Caglar; Zettl, Alex

    2010-03-01

    The easily accessible 2D electron gas in graphene provides an ideal platform on which to tune, via application of an electrostatic gate, the coupling between electronically ordered dopants deposited on its surface. To demonstrate this concept, we have measured arrays of superconducting clusters deposited on Graphene capable to induce via the proximity effect a gate-tunable superconducting transition. Using a simple fabrication procedure based on metal layer dewetting, doped graphene sheets can be decorated with a non percolating network on nanoscale tin clusters. This hybrid material displays a two-step superconducting transition. The higher transition step is gate independent and corresponds to the transition of the tin clusters to the superconducting state. The lower transition step towards a real zero resistance state exhibiting a well developped supercurrent, is strongly gate-tunable and is quantitatively described by Berezinskii-Kosterlitz-Thouless 2D vortex unbinding. Our simple self-assembly method and tunable coupling can readily be extended to other electronic order parameters such as ferro/antiferromagnetism, charge/spin density waves using similar decoration techniques. [1] B. M. Kessler, C.O. Girit, A. Zettl, and V. Bouchiat, Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets submitted to PRL, arXiv:0907.3661

  17. Materials for Flexible, Stretchable Electronics: Graphene and 2D Materials

    Kim, Sang Jin; Choi, Kyoungjun; Lee, Bora; Kim, Yuna; Hong, Byung Hee

    2015-07-01

    Recently, 2D materials have been intensively studied as emerging materials for future electronics, including flexible electronics, photonics, and electrochemical energy storage devices. Among representative 2D materials (such as graphene, boron nitride, and transition metal dichalcogenides) that exhibit extraordinary properties, graphene stands out in the flexible electronics field due to its combination of high electron mobility, high thermal conductivity, high specific surface area, high optical transparency, excellent mechanical flexibility, and environmental stability. This review covers the synthesis, transfer, and characterization methods of graphene and 2D materials and graphene's application to flexible devices as well as comparison with other competing materials.

  18. 2D Electron Gas with 100% Spin-Polarization in the (LaMnO 3 ) 2 /(SrTiO 3 ) 2 Superlattice under Uniaxial Strain

    Cossu, F.

    2014-07-28

    By first-principles calculations we investigate the structural, electronic, and magnetic properties of the (LaMnO3)2/(SrTiO3)2 superlattice. We find that a monoclinic C2h symmetry is energetically favorable and that the spins order ferromagnetically. Under both compressive and tensile uniaxial strain the electronic structure of the superlattice shows a half-metallic character. In particular, a fully spin-polarized two-dimensional electron gas, which traces back to the Ti 3dxy orbitals, is achieved under compressive uniaxial strain. The (LaMnO3)2/(SrTiO3)2 superlattice is analysed with respect to its structure, magnetism, and electronic properties. Our results demonstrate that uniaxial strain in an experimentally accessible range, both tensile and compressive, can be used to induce half-metallicity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. 2D electron cyclotron emission imaging at ASDEX Upgrade (invited)

    Classen, I. G. J. [Max Planck Institut fuer Plasmaphysik, 85748 Garching (Germany); FOM-Institute for Plasma Physics, Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Boom, J. E.; Vries, P. C. de [FOM-Institute for Plasma Physics, Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Suttrop, W.; Schmid, E.; Garcia-Munoz, M.; Schneider, P. A. [Max Planck Institut fuer Plasmaphysik, 85748 Garching (Germany); Tobias, B.; Domier, C. W.; Luhmann, N. C. Jr. [University of California at Davis, Davis, California 95616 (United States); Donne, A. J. H. [FOM-Institute for Plasma Physics, Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands); Jaspers, R. J. E. [Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands); Park, H. K. [POSTECH, Pohang, Gyeongbuk, 790-784 (Korea, Republic of); Munsat, T. [University of Colorado, Boulder, Colorado 80309 (United States)

    2010-10-15

    The newly installed electron cyclotron emission imaging diagnostic on ASDEX Upgrade provides measurements of the 2D electron temperature dynamics with high spatial and temporal resolution. An overview of the technical and experimental properties of the system is presented. These properties are illustrated by the measurements of the edge localized mode and the reversed shear Alfven eigenmode, showing both the advantage of having a two-dimensional (2D) measurement, as well as some of the limitations of electron cyclotron emission measurements. Furthermore, the application of singular value decomposition as a powerful tool for analyzing and filtering 2D data is presented.

  20. Energy level transitions of gas in a 2D nanopore

    Grinyaev, Yurii V., E-mail: grn@ispms.tsc.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Chertova, Nadezhda V., E-mail: chertova@ispms.tsc.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Psakhie, Sergei G., E-mail: sp@ispms.tsc.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation)

    2015-10-27

    An analytical study of gas behavior in a 2D nanopore was performed. It is shown that the temperature dependence of gas energy can be stepwise due to transitions from one size-quantized subband to another. Taking into account quantum size effects results in energy level transitions governed by the nanopore size, temperature and gas density. This effect leads to an abrupt change of gas heat capacity in the nanopore at the above varying system parameters.

  1. Energy level transitions of gas in a 2D nanopore

    An analytical study of gas behavior in a 2D nanopore was performed. It is shown that the temperature dependence of gas energy can be stepwise due to transitions from one size-quantized subband to another. Taking into account quantum size effects results in energy level transitions governed by the nanopore size, temperature and gas density. This effect leads to an abrupt change of gas heat capacity in the nanopore at the above varying system parameters

  2. Local 2D-2D tunneling in high mobility electron systems

    Pelliccione, Matthew; Sciambi, Adam; Bartel, John; Goldhaber-Gordon, David; Pfeiffer, Loren; West, Ken; Lilly, Michael; Bank, Seth; Gossard, Arthur

    2012-02-01

    Many scanning probe techniques have been utilized in recent years to measure local properties of high mobility two-dimensional (2D) electron systems in GaAs. However, most techniques lack the ability to tunnel into the buried 2D system and measure local spectroscopic information. We report scanning gate measurements on a bilayer GaAs/AlGaAs heterostructure that allows for a local modulation of tunneling between two 2D electron layers. We call this technique Virtual Scanning Tunneling Microscopy (VSTM) [1,2] as the influence of the scanning gate is analogous to an STM tip, except at a GaAs/AlGaAs interface instead of a surface. We will discuss the spectroscopic capabilities of the technique, and show preliminary results of measurements on a high mobility 2D electron system.[1] A. Sciambi, M. Pelliccione et al., Appl. Phys. Lett. 97, 132103 (2010).[2] A. Sciambi, M. Pelliccione et al., Phys. Rev. B 84, 085301 (2011).

  3. 2-D Imaging of Electron Temperature in Tokamak Plasmas

    By taking advantage of recent developments in millimeter wave imaging technology, an Electron Cyclotron Emission Imaging (ECEI) instrument, capable of simultaneously measuring 128 channels of localized electron temperature over a 2-D map in the poloidal plane, has been developed for the TEXTOR tokamak. Data from the new instrument, detailing the MHD activity associated with a sawtooth crash, is presented

  4. 2-D Imaging of Electron Temperature in Tokamak Plasmas

    T. Munsat; E. Mazzucato; H. Park; C.W. Domier; M. Johnson; N.C. Luhmann Jr.; J. Wang; Z. Xia; I.G.J. Classen; A.J.H. Donne; M.J. van de Pol

    2004-07-08

    By taking advantage of recent developments in millimeter wave imaging technology, an Electron Cyclotron Emission Imaging (ECEI) instrument, capable of simultaneously measuring 128 channels of localized electron temperature over a 2-D map in the poloidal plane, has been developed for the TEXTOR tokamak. Data from the new instrument, detailing the MHD activity associated with a sawtooth crash, is presented.

  5. Strain Engineering of the Electronic Structure of 2D Materials

    Frank, Otakar; del Corro, Elena; Pea-Álvarez, M.; Morales-García, A.; Bouša, M.; Řáhová, Jaroslava; Kavan, Ladislav; Kalbáč, Martin

    Brno : Tanger Ltd., 2015. s. 33-33. ISBN 978-80-87294-59-8. [Nanocon 2015. International Conference /7./. 14.10.2015-16.10.2015, Ostrava] R&D Projects: GA ČR GA14-15357S Institutional support: RVO:61388955 Keywords : graphene * electronic structure * 2D materials Subject RIV: CF - Physical ; Theoretical Chemistry

  6. Spin dependent 2D electron scattering by nanomagnets

    The 2D scattering problem of an electron by a magnetized nanoparticle is solved in the Born approximation with account of the dipole-dipole interaction of the magnetic moments of electron and nanomagnet. The scattering amplitudes in this problem are the two-component spinors. They are obtained as functions of the electron spin orientation, the electron energy and show anisotropy in scattering angle. The initially polarized beam of electrons scattered by the nanomagnet consists of electrons with no spin flipped and spin flipped. The majority of electrons with no spin flipped are scattered by small angles. The majority electrons with spin flipped are scattered in the vicinity of the scattering angles π/2 and 3π/2. This can be used as one more method of controlling the spin currents. - Research highlights: → The artificial namomagnets with gigantic magnetic moments strongly interact with spins of electrons. → In 2D geometry this interaction controls the electron-nanomagnet scattering. → The scattering amplitudes are two-component spinors. → The scattering lengths depend on orientation of magnetic moment of the nanomagnet, the electron spin, and the scattering angle. → This dependence can be used for controlling the spin currents.

  7. F2D: A two dimensional compressible gas flow code

    The F2D computer code is a general-purpose, two-dimensional, fully compressible thermal-fluids code that models most phenomena found in experimental environments with coupled fluid flow and heat transfer. The code solves momentum, continuity, gas energy, and structure energy equations, simultaneously utilizing a predictor-corrector solution algorithm. The F2D code applied to a particle-bed reactor operating at 5 MW/L with a flow-control cold frit, revealed a skew in the temperature contours caused by two-dimensional flow effects. A thermal-fluid stability analysis of particle-bed and NERVA type reactors reveals similar behavior for the stability threshold

  8. Relativistic quantum Hall conductivity for 3D and 2D electron plasma in an external magnetic field

    The complete antisymmetric form of the conductivity tensor in the static limit, as well as the expression for the Hall conductivity, is obtained for the relativistic 3D and 2D electron gas in a magnetic field. The non-relativistic 2D limit is also discussed. The typical step form of the 2D Hall conductivity at zero temperature is obtained under the simple hypothesis of constancy of the chemical potential. (author). 6 refs, 1 fig

  9. 2D-MoO3 nanosheets for superior gas sensors

    Ji, Fangxu; Ren, Xianpei; Zheng, Xiaoyao; Liu, Yucheng; Pang, Liuqing; Jiang, Jiaxing; Liu, Shengzhong (Frank)

    2016-04-01

    By taking advantages of both grinding and sonication, an effective exfoliation process is developed to prepare two-dimensional (2D) molybdenum oxide (MoO3) nanosheets. The approach avoids high-boiling-point solvents that would leave a residue and cause aggregation. Gas sensors fabricated using the 2D-MoO3 nanosheets provide a significantly enhanced chemical sensor performance. Compared with the sensors using bulk MoO3, the response of the 2D-MoO3 sensor increases from 7 to 33; the sensor response time is reduced from 27 to 21 seconds, and the recovery time is shortened from 26 to 10 seconds. We attribute the superior performance to the 2D-structure with a much increased surface area and reactive sites.By taking advantages of both grinding and sonication, an effective exfoliation process is developed to prepare two-dimensional (2D) molybdenum oxide (MoO3) nanosheets. The approach avoids high-boiling-point solvents that would leave a residue and cause aggregation. Gas sensors fabricated using the 2D-MoO3 nanosheets provide a significantly enhanced chemical sensor performance. Compared with the sensors using bulk MoO3, the response of the 2D-MoO3 sensor increases from 7 to 33; the sensor response time is reduced from 27 to 21 seconds, and the recovery time is shortened from 26 to 10 seconds. We attribute the superior performance to the 2D-structure with a much increased surface area and reactive sites. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00880a

  10. Importance of Overpressure in 2D Gas Hydrate Modeling

    Hauschildt, J.; Unnithan, V.

    2005-12-01

    Numerical models for sub-seafloor gas hydrate formation [1],[2],[3] which describe the driving fluid transport processes only in the vertical direction, restrict the computationally expensive problem to one dimension. This assumption is only valid in regions where permeable sediments induce no overpressure and where there is little lateral variation of physical properties and boundary conditions. Local accumulations of gas hydrates or authigenic carbonates can significantly reduce the porosity and permeability. In combination with topographic and structural features, subtle but important deviations from the 1D model are considered to occur. This poster shows results obtained from a 2D finite difference model developed for describing the evolution of the gas hydrate zone in structurally complex areas. The discretisation of the terms governing the thermodynamic and transport processes is implemented explicitely in time for the advection and diffusion processes, but implicitely for phase transitions. Although the time scales for transport and phase transitions can differ by several orders of magnitude, this scheme allows for an efficient computation for model runs both over the system's equilibration period in the order of 107 yr or to resolve the effects of sea-level changes within 103 yr. A sensitivity analysis confines the parameter space relevant for hydrate formation influenced by lateral fluid flow, and results for the predicted deviations from a multi-1D model for high gas hydrate fractions and fluid flow rates are presented. References [1] M.K. Davie and B.A. Buffett. Sources of methane for marine gas hydrate: inferences from a comparison of observations and numerical models. Earth and Planetary Science Letters, 206:51-63, 2003. [2] W. Xu and C. Ruppell. Predicting the occurrence, distribution, and evolution of methane hydrate in porous marine sediments. Journal of Geohphysical Research, (B3):5081-5095, 1999. [3] J.B. Klauda and S.I. Sandler. Predictions of

  11. 2D scattering of unpolarized beams of electrons by charged nanomagnets

    Senbeta, Teshome, E-mail: teshearada@yahoo.com [Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa (Ethiopia); Mal' nev, V.N., E-mail: vnmalnev@aau.edu.et [Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa (Ethiopia)

    2012-07-15

    2D spin-dependent scattering of slow unpolarized beams of electrons by charged nanomagnets is analyzed in the Born approximation. The obtained scattering lengths are larger than those from the neutral nanomagnets approximately by one order. It is shown that for particular parameters of the system it is possible to polarize completely the scattered electrons in a narrow range of scattering angles. The most suitable system for realization of these effects is 2D Si electron gas with immersed nanomagnets. - Highlights: Black-Right-Pointing-Pointer We study 2D spin dependent electron scattering by charged nanomagnets. Black-Right-Pointing-Pointer The applicability of the Born approximation to the problem is discussed. Black-Right-Pointing-Pointer Unpolarized incident beams used to obtain completely polarized scattered electrons. Black-Right-Pointing-Pointer The study shows peculiarities of 2D spin dependent scattering enhanced by Coulomb potential. Black-Right-Pointing-Pointer The result obtained can be used as one method of controlling spin currents.

  12. Transport Properties of 2D-Electron Gas in a InGaAs/GaAs DQW in a Vicinity of Low Magnetic-Field-Induced Insulator-Quantum Hall Liquid Transition

    Arapov, Yu. G.; Yakunin, M. V.; Gudina, S. V.; Harus, G. I.; Neverov, V. N.; Shelushinina, N. G.; Podgornyh, S. M.; Uskova, E. A.; Zvonkov, B. N.

    2007-04-01

    The resistivity ρ of low mobility dilute 2D-elecron gas in a InGaAs/GaAs double quantum well (DQW) exhibits the monotonic "insulating-like" temperature dependence (dρ/dT 0.1) for our samples. We observed the coexistence of both the quantum Hall (QH) effect for the filling factors v = 2, 4 and the low magnetic field insulator — QH liquid (with v = 10) transition.

  13. Metal Decoration Effects on the Gas-Sensing Properties of 2D Hybrid-Structures on Flexible Substrates

    Byungjin Cho

    2015-09-01

    Full Text Available We have investigated the effects of metal decoration on the gas-sensing properties of a device with two-dimensional (2D molybdenum disulfide (MoS2 flake channels and graphene electrodes. The 2D hybrid-structure device sensitively detected NO2 gas molecules (>1.2 ppm as well as NH3 (>10 ppm. Metal nanoparticles (NPs could tune the electronic properties of the 2D graphene/MoS2 device, increasing sensitivity to a specific gas molecule. For instance, palladium NPs accumulate hole carriers of graphene/MoS2, electronically sensitizing NH3 gas molecules. Contrarily, aluminum NPs deplete hole carriers, enhancing NO2 sensitivity. The synergistic combination of metal NPs and 2D hybrid layers could be also applied to a flexible gas sensor. There was no serious degradation in the sensing performance of metal-decorated MoS2 flexible devices before/after 5000 bending cycles. Thus, highly sensitive and endurable gas sensor could be achieved through the metal-decorated 2D hybrid-structure, offering a useful route to wearable electronic sensing platforms.

  14. Optical and Electronic Properties of 2D Graphitic Carbon-Nitride and Carbon Enriched Alloys

    Therrien, Joel; Li, Yancen; Schmidt, Daniel; Masaki, Michael; Syed, Abdulmannan

    The two-dimensional form of graphitic carbon-nitride (gCN) has been successfully synthesized using a simple CVD process. In it's pure form, the carbon to nitrogen ratio is 0.75. By adding a carbon bearing gas to the growth environment, the C/N ratio can be increased, ultimately reaching the pure carbon form: graphene. Unlike attempts at making a 2D alloy system out of BCN, the CN system does not suffer from phase segregation and thus forms a homogeneous alloy. The synthesis approach and electronic and optical properties will be presented for the pure gCN and a selection of alloy compositions.

  15. Sub-electron Charge Relaxation via 2D Hopping Conductors

    Kinkhabwala, Yusuf A.; Likharev, Konstantin K.

    2005-01-01

    We have extended Monte Carlo simulations of hopping transport in completely disordered 2D conductors to the process of external charge relaxation. In this situation, a conductor of area $L \\times W$ shunts an external capacitor $C$ with initial charge $Q_i$. At low temperatures, the charge relaxation process stops at some "residual" charge value corresponding to the effective threshold of the Coulomb blockade of hopping. We have calculated the r.m.s$.$ value $Q_R$ of the residual charge for a...

  16. A scintillating gas detector for 2D dose measurements in clinical carbon beams

    A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies

  17. A scintillating gas detector for 2D dose measurements in clinical carbon beams

    Seravalli, E.; de Boer, M.; Geurink, F.; Huizenga, J.; Kreuger, R.; Schippers, J. M.; van Eijk, C. W. E.; Voss, B.

    2008-09-01

    A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

  18. 2D semiclassical model for high harmonic generation from gas

    陈黎明; 余玮; 张杰; 陈朝阳; 江文勉

    2000-01-01

    The electron behavior in laser field is described in detail. Based on the 1D semiclassical model, a 20 semiclassical model is proposed analytically using 3D DC-tunneling ionization theory. Lots of harmonic features are explained by this model, including the analytical demonstration of the maximum electron energy 3.17 Up. Finally, some experimental phenomena such as the increase of the cutoff harmonic energy with the decrease of pulse duration and the "anomalous" fluctuations in the cutoff region are explained by this model.

  19. Final LDRD report : the physics of 1D and 2D electron gases in III-nitride heterostructure NWs.

    Armstrong, Andrew M.; Arslan, Ilke (Sandia National Laboratories, Livermore, CA); Upadhya, Prashanth C. (Los Alamos National Laboratory, Los Alamos, NM); Morales, Eugenia T. (Sandia National Laboratories, Livermore, CA); Leonard, Francois Leonard (Sandia National Laboratories, Livermore, CA); Li, Qiming; Wang, George T.; Talin, Albert Alec (Sandia National Laboratories, Livermore, CA); Prasankumar, Rohit P. (Los Alamos National Laboratory, Los Alamos, NM); Lin, Yong

    2009-09-01

    The proposed work seeks to demonstrate and understand new phenomena in novel, freestanding III-nitride core-shell nanowires, including 1D and 2D electron gas formation and properties, and to investigate the role of surfaces and heterointerfaces on the transport and optical properties of nanowires, using a combined experimental and theoretical approach. Obtaining an understanding of these phenomena will be a critical step that will allow development of novel, ultrafast and ultraefficient nanowire-based electronic and photonic devices.

  20. 2D-sensitive hpxe gas proportional scintillation counter concept for nuclear medical imaging purposes

    The operation and first images of a high pressure xenon Gas Proportional Scintillation Counter (GPSC) are presented. In this setup, primary electrons produced by the absorption of X- or γ-rays in the gas medium drift to a region where the electric field is set to a value above the gas scintillation threshold, the scintillation region. The primary ionization signal is amplified through the electroluminescence produced along the electron drift in this region. A Micro-Hole and Strip Plate covered with CsI (CsI-MHSP) is used as the photosensor for the scintillation readout. The 2D capability of the CsI-MHSP photosensor is achieved by means of two orthogonal resistive lines interconnecting the strips patterned on both surfaces of the MHSP. The interaction position of the incident radiation can be obtained by determining the centroid of the photosensor area irradiated by the electroluminescence pulse. This centroid is obtained from the amplitude of the charge pulses collected at both ends of the resistive lines. Preliminary analyses of the first images obtained with electroluminescence signals at xenon pressures up to 3 bar indicate a position resolution capability of about 1.2 mm at 2.9 bar, for 59.6 keV γ-photons.

  1. Can positron 2D-ACAR resolve the electronic structure of high-Tc superconductors

    In this paper, the authors examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-Tc cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-Tc superconductors, are given. The authors briefly review recent 2D-ACAR experiments on YBa2Cu3O7-x, Bi2Sr2CaCuO8+δ and La2-xSrxCuO4. The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-Tc cuprate superconductors

  2. 2D electron density profile measurement in tokamak by laser-accelerated ion-beam probe

    A new concept of Heavy Ion Beam Probe (HIBP) diagnostic has been proposed, of which the key is to replace the electrostatic accelerator of traditional HIBP by a laser-driven ion accelerator. Due to the large energy spread of ions, the laser-accelerated HIBP can measure the two-dimensional (2D) electron density profile of tokamak plasma. In a preliminary simulation, a 2D density profile was reconstructed with a spatial resolution of about 2 cm, and with the error below 15% in the core region. Diagnostics of 2D density fluctuation is also discussed

  3. 2 D patterns of soil gas diffusivity , soil respiration, and methane oxidation in a soil profile

    Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

    2015-04-01

    The apparent gas diffusion coefficient in soil (DS) is an important parameter describing soil aeration, which makes it a key parameter for root growth and gas production and consumption. Horizontal homogeneity in soil profiles is assumed in most studies for soil properties - including DS. This assumption, however, is not valid, even in apparently homogeneous soils, as we know from studies using destructive sampling methods. Using destructive methods may allow catching a glimpse, but a large uncertainty remains, since locations between the sampling positions cannot be analyzed, and measurements cannot be repeated. We developed a new method to determine in situ the apparent soil gas diffusion coefficient in order to examine 2 D pattern of DS and methane oxidation in a soil profile. Different tracer gases (SF6, CF4, C2H6) were injected continuously into the subsoil and measured at several locations in the soil profile. These data allow for modelling inversely the 2 D patterns of DS using Finite Element Modeling. The 2D DS patterns were then combined with naturally occurring CH4 and CO2 concentrations sampled at the same locations to derive the 2D pattern of soil respiration and methane oxidation in the soil profile. We show that methane oxidation and soil respiration zones shift within the soil profile while the gas fluxes at the surface remain rather stable during a the 3 week campaign.

  4. Nano-scale electronic and optoelectronic devices based on 2D crystals

    Zhu, Wenjuan

    In the last few years, the research community has been rapidly growing interests in two-dimensional (2D) crystals and their applications. The properties of these 2D crystals are diverse -- ranging from semi-metal such as graphene, semiconductors such as MoS2, to insulator such as boron nitride. These 2D crystals have many unique properties as compared to their bulk counterparts due to their reduced dimensionality and symmetry. A key difference is the band structures, which lead to distinct electronic and photonic properties. The 2D nature of the material also plays an important role in defining their exceptional properties of mechanical strength, surface sensitivity, thermal conductivity, tunable band-gap and their interaction with light. These unique properties of 2D crystals open up a broad territory of applications in computing, communication, energy, and medicine. In this talk, I will present our work on understanding the electrical properties of graphene and MoS2, in particular current transport and band-gap engineering in graphene, interface between gate dielectrics and graphene, and gap states in MoS2. I will also present our work on the nano-scale electronic devices (RF and logic devices) and photonic devices (plasmonic devices and photo-detectors) based on these 2D crystals.

  5. 2-D studies of Relativistic electron beam plasma instabilities in an inhomogeneous plasma

    Shukla, Chandrashekhar; Patel, Kartik

    2015-01-01

    Relativistic electron beam propagation in plasma is fraught with several micro instabilities like two stream, filamentation etc., in plasma. This results in severe limitation of the electron transport through a plasma medium. Recently, however, there has been an experimental demonstration of improved transport of Mega Ampere of electron currents (generated by the interaction of intense laser with solid target) in a carbon nanotube structured solid target [Phys. Rev Letts. 108, 235005 (2012)]. This then suggests that the inhomogeneous plasma (created by the ionization of carbon nano tube structured target) helps in containing the growth of the beam plasma instabilities. This manuscript addresses this issue with the help of a detailed analytical study and simulations with the help of 2-D Particle - In - Cell code. The study conclusively demonstrates that the growth rate of the dominant instability in the 2-D geometry decreases when the plasma density is chosen to be inhomogeneous, provided the scale length 1/ks...

  6. Charge Transport in a Spin-Polarized 2D Electron System in Silicon

    Knyazev, D. A.; Omelyanovskii, O. E.; Dormidontov, A. S.; Pudalov, V.M.

    2006-01-01

    The temperature dependences of the conductivity \\sigma(T) for strongly interacting 2D electron system in silicon have been analyzed both in zero magnetic field and in spin-polarizing magnetic field of 14.2T, parallel to the sample plane. Measurements were carried out in a wide temperature range (1.4-9)K, in the ballistic regime of electron-electron interaction, i.e., for T\\tau > 1. In zero magnetic field, the data obtained for \\sigma(T) are quantitatively described by the theory of interactio...

  7. Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

    Guell, A. G.; Ebejer, N.; Snowden, M. E.; McKelvey, K.; J. V. Macpherson; Unwin, P. R.

    2012-01-01

    Carbon nanotubes have attracted considerable interest for electrochemical, electrocatalytic, and sensing applications, yet there remains uncertainty concerning the intrinsic electrochemical (EC) activity. In this study, we use scanning electrochemical cell microscopy (SECCM) to determine local heterogeneous electron transfer (HET) kinetics in a random 2D network of single-walled carbon nanotubes (SWNTs) on an Si/SiO2 substrate. The high spatial resolution of SECCM, which employs a mobile nano...

  8. 2D momentum distribution of electron in transfer ionization of helium atom by fast proton

    2D distribution of momentum components of the ejected electron in the reaction H+ +He → H+He2++e at 630 keV proton is studied both theoretically and experimentally. This allows to unambiguously identify contributions from the shake-off and binary encounter mechanisms of transfer ionization. It is shown that the results are highly sensitive to the quality of the initial-state wave function.

  9. 2D PIC simulations of collisional transport of relativistic electrons in dense plasma

    Héron A.

    2013-11-01

    Full Text Available We report results of a series of simulations about electron transport in plasma close to solid density performed with a collisional 2D3V PIC code and compare the results to published ones obtained using hybrid codes. We show that the dispersion of energetic particles remains similar to the one observed in the collisionless case and discuss and compare our results in the light of hybrid codes.

  10. Theory of a four-electron 2-D system in a strong magnetic field

    An orthogonal and complete set for relative motion of four-electron 2-D system in strong magnetic field is given, the energy of ground state of relative motion is calculated. This paper also calculates the energy of ground state whose maximum of single electron angular momentum is limited by the degeneracy under a given magnetic field, obtains the energy minimums corresponding to a fractional quantized Hall effect of 2/5, 2/7, and from it the physical meaning of 'magic number' is interpreted. (author)

  11. Polarization induced 2D hole gas in GaN/AlGaN heterostructures

    Hackenbuchner, S.; Majewski, J. A.; Zandler, G.; Vogl, P.

    2001-09-01

    The generation of high density 2D hole gases is crucial for further progress in the electronic and optoelectronic nitride devices. In this paper, we present systematic theoretical studies of Mg-doped GaN/AlGaN gated heterostructures and superlattices. Our calculations are based on a self-consistent solution of the multiband k. p Schrödinger and Poisson equation and reveal that the hole 2D sheet density is mainly determined by the polarization induced interface charges. For an aluminium concentration of 30%, the induced hole density in the heterostructure can reach values up to 1.5×10 13 cm -2. In the GaN/AlGaN superlattices, the hole sheet density increases with the superlattice period and saturates for a period of 40 nm at a value of 1.5×10 13 cm -2.

  12. Coherence properties of a 2D trapped Bose gas around the superfluid transition

    Plisson, T; Holzmann, M; Salomon, G; Aspect, Alain; Bouyer, Philippe; Bourdel, Thomas

    2011-01-01

    We measure the momentum distribution of a 2D trapped Bose gas and observe the increase of the range of coherence around the Berezinskii-Kosterlitz-Thouless (BKT) transition. We quantitatively compare our observed profiles to both a Hartee-Fock mean-field theory and to quantum Monte-Carlo simulations. In the normal phase, we already observe a sharpening of the momentum distribution. This behavior is partially captured in a mean-field approach, in contrast to the physics of the BKT transition.

  13. Laser Absorption spectrometer instrument for tomographic 2D-measurement of climate gas emission from soils

    Seidel, Anne; Wagner, Steven; Dreizler, Andreas; Ebert, Volker

    2014-05-01

    One of the most intricate effects in climate modelling is the role of permafrost thawing during the global warming process. Soil that has formerly never totally lost its ice cover now emits climate gases due to melting processes[1]. For a better prediction of climate development and possible feedback mechanisms, insights into physical procedures (like e.g. gas emission from underground reservoirs) are required[2]. Therefore, a long-term quantification of greenhouse gas concentrations (and further on fluxes) is necessary and the related structures that are responsible for emission need to be identified. In particular the spatial heterogeneity of soils caused by soil internal structures (e.g. soil composition changes or surface cracks) or by surface modifications (e.g. by plant growth) generate considerable complexities and difficulties for local measurements, for example with soil chambers. For such situations, which often cannot be avoided, a spatially resolved 2D-measurement to identify and quantify the gas emission from the structured soil would be needed, to better understand the influence of the soil sub-structures on the emission behavior. Thus we designed a spatially scanning laser absorption spectrometer setup to determine a 2D-gas concentration map in the soil-air boundary layer. The setup is designed to cover the surfaces in the range of square meters in a horizontal plane above the soil to be investigated. Existing field instruments for gas concentration or flux measurements are based on point-wise measurements, so structure identification is very tedious or even impossible. For this reason, we have developed a tomographic in-situ instrument based on TDLAS ('tunable diode laser absorption spectroscopy') that delivers absolute gas concentration distributions of areas with 0.8m × 0.8m size, without any need for reference measurements with a calibration gas. It is a simple and robust device based on a combination of scanning mirrors and reflecting foils, so

  14. 2D-hybrid particle model with non-linear electron distribution

    A 2D, hybrid (particle-ion, fluid-electron) simulation code characterized by the solution of the non-linear modified Poisson equation, which results assuming the Boltzmann distribution for the electrons, is presented. The field solution is achieved through an iterative procedure. Anyhow a new scheme is considered. The potential is not obtained by directly solving the finite difference equation but via the Green's function method. The procedure begins with the first guess for the potential. This is found through the solution of the linearized modified Poisson equation. The Green's function for this equation, in the 2D case which is considered, can be found analytically in terms of the Newmann functions. Once the potential corresponding to the linearized modified Poisson equation is known, the first approximation of the electron (Boltzmann) distribution can be calculated. This distribution, plus the one given by the (particle) ions, is considered as the source term for the Poisson equation (which now is not modified since the fluid electron component is taken into account in the source term itself). The solution of this Poisson equation gives the second approximation of the electric potential and is still obtained via the Green's function method (as it comes from the Coulomb law, modified for the 2D case). Each time step this procedure can be iterated according to the desired accuracy. The last iteration cycle is different: in fact the direct solution for the electric field can be obtained, without numerical differencing from the potential. It is sufficient in this case to consider the electric field Green's functions (x- and y-component) for the Poisson equation (in place of the electric potential Green's function). The first results obtained with this new code are here presented and compared with previous simulation runs based on a linearized Boltzmann distribution model. 3 refs

  15. Electronic interaction effects in rare-earth alloys from 2D-ACAR experiments

    Measurement of the two dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) complemented with ab-initio calculations can provide decisive information about the character of the f-electrons in rare earth compounds and are the prerequisite to the study of electron correlations. We provide examples of systems where good approximations of the archetype f-electron localized and f-electron itinerant behaviours, apply. i) In the case of the antiferromagnetic heavy fermion and superconductor CeIn3 the multisheet Fermi Surface (FS), reconstructed from our measurements in the paramagnetic phase, agrees closely with the predictions of band structure calculations regarding the Ce 4f electrons as fully localized. ii) On the other hand, our studies of the antiferromagnet actinide based UGa3 in the paramagnetic phase, compared with calculations which include the effects due to the non uniform positron density and the electron-positron correlations, produce a substantial evidence that an unconstrained 5f-electron itinerant description applies. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Electronic control of edge-mode spectrum of integer-hall-effect 2d electron waveguides

    Kouzaev, Guennadi A.

    2015-01-01

    In this paper, the control of the edge-mode spectrum of integer-Hall-effect 2D waveguides by electric field is proposed and modeled with the effective mass approach. Under certain found conditions, the applied transversal electric field allows refining the modal spectrum from non-localized waves, and, additionally, it can switch the edge-mode from the propagating to the evanescent state, and it is interesting in the design of the edge-mode off and on logic components. These waveguides, arbitr...

  17. Electron spectroscopy of rubber and resin-based composites containing 2D carbon

    Composite materials with 2D carbon (graphene and/or single wall carbon nanotubes) are very promising due to their extraordinary electrical and mechanical properties. Graphene and natural rubber composites, which may be used for the gaskets or sealants, were prepared by ultrasonically assisted latex-mixing exfoliation and in-situ reduction process, with two vulcanization approaches: roll-mixing and hot-pressing. Also the resin-based composites, filled with micro-particles of Ag and graphene or carbon nanotubes, have been studied. The standards for the compositional characterization of these materials still are not established. In addition to the mostly used techniques, such as Raman spectroscopy and electron microscopy, also Auger electron spectroscopy can be employed for the identification of graphene. In this study, the shape of C KVV peak, excited by electron beam and X-ray photons, has been investigated in different composite materials containing graphene and carbon nanotubes. A spectroscopic method for 2D carbon recognition, based on the Dx parameter which is determined from C KVV signal excited by X-ray photons, was proposed and verified. Even a small content of graphene in different types of composites was sufficient for this recognition due to the dominating presence of graphene on the surface of composites. - Highlights: • Chemical composition of the rubber composites was determined by XPS. • Auger spectrum of carbon was used for graphene identification in composites. • Small content of graphene was sufficient for its recognition from the D parameter

  18. Electron spectroscopy of rubber and resin-based composites containing 2D carbon

    Kaciulis, S., E-mail: saulius.kaciulis@ismn.cnr.it [Institute for the Study of Nanostructured Materials, ISMN-CNR, P.O. Box 10, Monterotondo Stazione, 00015 Roma (Italy); Mezzi, A.; Balijepalli, S.K. [Institute for the Study of Nanostructured Materials, ISMN-CNR, P.O. Box 10, Monterotondo Stazione, 00015 Roma (Italy); Lavorgna, M. [Institute of Polymers, Composites and Biomaterials, IPCB-CNR, P.le Fermi, 80055 Napoli (Italy); Xia, H.S. [State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, 610065 Sichuan (China)

    2015-04-30

    Composite materials with 2D carbon (graphene and/or single wall carbon nanotubes) are very promising due to their extraordinary electrical and mechanical properties. Graphene and natural rubber composites, which may be used for the gaskets or sealants, were prepared by ultrasonically assisted latex-mixing exfoliation and in-situ reduction process, with two vulcanization approaches: roll-mixing and hot-pressing. Also the resin-based composites, filled with micro-particles of Ag and graphene or carbon nanotubes, have been studied. The standards for the compositional characterization of these materials still are not established. In addition to the mostly used techniques, such as Raman spectroscopy and electron microscopy, also Auger electron spectroscopy can be employed for the identification of graphene. In this study, the shape of C KVV peak, excited by electron beam and X-ray photons, has been investigated in different composite materials containing graphene and carbon nanotubes. A spectroscopic method for 2D carbon recognition, based on the D{sub x} parameter which is determined from C KVV signal excited by X-ray photons, was proposed and verified. Even a small content of graphene in different types of composites was sufficient for this recognition due to the dominating presence of graphene on the surface of composites. - Highlights: • Chemical composition of the rubber composites was determined by XPS. • Auger spectrum of carbon was used for graphene identification in composites. • Small content of graphene was sufficient for its recognition from the D parameter.

  19. Wavelet characterization of 2D turbulence and intermittency in magnetized electron plasmas

    Romé, M.; Chen, S.; Maero, G.

    2016-06-01

    A study of the free relaxation of turbulence in a two-dimensional (2D) flow is presented, with a focus on the role of the initial vorticity conditions. Exploiting a well-known analogy with 2D inviscid incompressible fluids, the system investigated here is a magnetized pure electron plasma. The dynamics of this system are simulated by means of a 2D particle-in-cell code, starting from different spiral density (vorticity) distributions. A wavelet multiresolution analysis is adopted, which allows the coherent and incoherent parts of the flow to be separated. Comparison of the turbulent evolution in the different cases is based on the investigation of the time evolution of statistical properties, including the probability distribution functions and structure functions of the vorticity increments. It is also based on an analysis of the enstrophy evolution and its spectrum for the two components. In particular, while the statistical features assess the degree of flow intermittency, spectral analysis allows us not only to estimate the time required to reach a state of fully developed turbulence, but also estimate its dependence on the thickness of the initial spiral density distribution, accurately tracking the dynamics of both the coherent structures and the turbulent background. The results are compared with those relevant to annular initial vorticity distributions (Chen et al 2015 J. Plasma Phys. 81 495810511).

  20. Hall-Effect Thruster Simulations with 2-D Electron Transport and Hydrodynamic Ions

    Mikellides, Ioannis G.; Katz, Ira; Hofer, Richard H.; Goebel, Dan M.

    2009-01-01

    A computational approach that has been used extensively in the last two decades for Hall thruster simulations is to solve a diffusion equation and energy conservation law for the electrons in a direction that is perpendicular to the magnetic field, and use discrete-particle methods for the heavy species. This "hybrid" approach has allowed for the capture of bulk plasma phenomena inside these thrusters within reasonable computational times. Regions of the thruster with complex magnetic field arrangements (such as those near eroded walls and magnets) and/or reduced Hall parameter (such as those near the anode and the cathode plume) challenge the validity of the quasi-one-dimensional assumption for the electrons. This paper reports on the development of a computer code that solves numerically the 2-D axisymmetric vector form of Ohm's law, with no assumptions regarding the rate of electron transport in the parallel and perpendicular directions. The numerical challenges related to the large disparity of the transport coefficients in the two directions are met by solving the equations in a computational mesh that is aligned with the magnetic field. The fully-2D approach allows for a large physical domain that extends more than five times the thruster channel length in the axial direction, and encompasses the cathode boundary. Ions are treated as an isothermal, cold (relative to the electrons) fluid, accounting for charge-exchange and multiple-ionization collisions in the momentum equations. A first series of simulations of two Hall thrusters, namely the BPT-4000 and a 6-kW laboratory thruster, quantifies the significance of ion diffusion in the anode region and the importance of the extended physical domain on studies related to the impact of the transport coefficients on the electron flow field.

  1. Dosimetric verification of gated delivery of electron beams using a 2D ion chamber array

    S A Yoganathan

    2015-01-01

    Full Text Available The purpose of this study was to compare the dosimetric characteristics; such as beam output, symmetry and flatness between gated and non-gated electron beams. Dosimetric verification of gated delivery was carried for all electron beams available on Varian CL 2100CD medical linear accelerator. Measurements were conducted for three dose rates (100 MU/min, 300 MU/min and 600 MU/min and two respiratory motions (breathing period of 4s and 8s. Real-time position management (RPM system was used for the gated deliveries. Flatness and symmetry values were measured using Imatrixx 2D ion chamber array device and the beam output was measured using plane parallel ion chamber. These detector systems were placed over QUASAR motion platform which was programmed to simulate the respiratory motion of target. The dosimetric characteristics of gated deliveries were compared with non-gated deliveries. The flatness and symmetry of all the evaluated electron energies did not differ by more than 0.7 % with respect to corresponding non-gated deliveries. The beam output variation of gated electron beam was less than 0.6 % for all electron energies except for 16 MeV (1.4 %. Based on the results of this study, it can be concluded that Varian CL2100 CD is well suitable for gated delivery of non-dynamic electron beams.

  2. Advanced 2D and 3D Electron Microscopy Analysis of Clay/PP Nanocomposites

    Mosca, Alessandra; Roberts, Ashley; Daviðsdóttir, Svava;

    2011-01-01

    the improved macroscopic properties of nanocomposites. In this work, a clay/PP nanocomposite is studied by 2D bright field transmission electron microscopy (TEM) and 3D focussed ion beam – field emission gun scanning electron microscopy (FIB/FEG SEM). Materials and Methods A clay/polymer nanocomposite...... consisting of 3 wt% modified clay in a PP matrix was studied. Prior to microscopy analyses, SEM or TEM samples were cryo-microtomed to a flat surface or thin sections (70 nm), respectively. An FEI Titan T20 TEM microscope operating at 200 kV was used for 2D imaging. An FEI Helios focussed ion beam (FIB......) equipped with field emission gun (FEG) and through lens detector (TLD) was used for high resolution 3D imaging of the material via slice-and-view technique [2]. Image analysis was performed using Matlab. Results and Discussion Figure 1 (a) shows a TEM micrograph of a clay/PP nanocomposite, where the clay...

  3. Distinguishing electronic and vibronic coherence in 2D spectra by their temperature dependence

    Perlík, Václav; Šanda, František; Hauer, Jürgen

    2013-01-01

    Long-lived oscillations in 2D spectra of chlorophylls are at the heart of an ongoing debate. Their physical origin is either a multi-pigment effect, such as excitonic coherence, or primarily stems from localized vibrations. In the present work, we analyze distinguishing characteristics of relative phase difference measured between diagonal- and cross-peak oscillations. While direct discrimination between the two scenarios is obscured when peaks overlap, their sensitivity to temperature provides a stronger argument. We show that vibrational (vibronic) oscillations change relative phase with temperature, while electronic oscillations are only weakly dependent. This highlights that studies of relative phase difference as a function of temperature provide a clear and easily accessible method to distinguish between vibrational and electronic coherences.

  4. Broadband 2D Electronic Spectroscopy Reveals Coupling Between Dark 1Bu- State of Carotenoid and Qx State of Bacteriochlorophyll

    Scholes Gregory D.

    2013-03-01

    Full Text Available The study of LH2 protein of purple bacteria by broadband 2D electronic spectroscopy is presented. The dark 1Bu- carotenoid state is directly observed in 2D spectra and its role in carotenoid-bacteriochlorophyll interaction is discussed.

  5. A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds

    Li, Tingwen; Zhang, Yongmin

    2013-10-11

    Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.

  6. Electron Cyclotron Power Losses in ITER for 2D Profile of Magnetic Field

    Full text: Recent comparison of numeric codes SNECTR, CYTRAN, CYNEQ and EXACTEC for calculating the 1D distribution, over magnetic flux surfaces, of the net electron cyclotron (EC) radiated power density, Pec(ρ), was carried out for a flat 1D profile of total magnetic field, which is an average over each magnetic surface and is used in 1.5D transport models: Btot(ρ) = BT (Ro) = Bo, vacuum toroidal magnetic field on toroid's axis. However, the predicted rise of Te in steady-state operation regimes in ITER and future reactors requires better accuracy of Pec(ρ) calculations, especially in the plasma hot core. Here we take into account the inhomogeneity of magnetic field in 2D approximation in the modified code CYNEQ. We compare three approximations of the magnetic field profile: (i) 2D-magnetic field B(R, Z); (ii) 1D - flux surface averaged magnetic field B(ρ)= (B(R, Z)); (iii) 0D - homogeneous magnetic field B = Bo. It is shown that, for the same plasma parameters expected in ITER, the Pec(ρ) profiles in the cases (i) and (ii) are very close, being lower than Pec(ρ) in the central plasma in the case of B = Bo = 5.3 T. In particular, for the enhanced confinement scenario, the decrease reaches ∼ 25%. The above effect has to be taken into account in the 1.5D transport codes when modeling the steady-state regimes of ITER operation. When central temperature increases to ∼ 30 keV the local EC power loss becomes a substantial part of heating from fusion alphas and exceeds the auxiliary heating from neutral beam. On the other hand, fast increase of Pec(0) with temperature has a positive impact on stabilization of fusion burning. Thus, for reactor scale parameters, accurate simulations of nonlocal heat transport by EC waves requires self-consistent 1.5D calculations of plasma parameters with 2D equilibrium. Meanwhile the EC energy transport has sufficient accuracy with 1D surface-averaged magnetic field B(ρ)= (B(R, Z)), derived from self-consistent 1.5D simulations

  7. PICLE: a 2-D code for laser-beam - gas-jet interaction studies

    A heat transport hydrodynamic PIC code was adapted for application to the KMSF gas-jet experiments. The input material density profile was changed from the original solid slab geometry to a cylindrically symmetric profile modeling the gas-jet plume. The target material was changed from the original Z = 1 to arbitrary Z. Energy deposition was modified to include inverse bremsstrahlung and resonance absorption. Preliminary results indicate electron thermal conduction dominates over mass flow for times up to about the laser pulse length. Electron thermal conduction is seen to vary between classical and flux-limited values spatially and temporally according to plasma conditions. Applications of this code, entitled PICLE (Particle-In-Cell Laser Equipment code), to absorption and flux-limit parameter studies are described. A source listing and sample input deck are included

  8. Positron 2D-ACAR experiments and electron-positron momentum density in YBa2Cu3OP7-x

    This paper discusses positron annihilation (2D-ACAR) measurements in the c-projection on an untwinned metallic single crystal of YBa2Cu3O7-x as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a background corrected experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface

  9. An analytic approach to 2D electronic PE spectra of molecular systems

    Graphical abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems using direct calculation from electronic Hamiltonians allows peak classification from 3P-PE spectra dynamics. Display Omitted Highlights: → RWA approach to electronic photon echo. → A straightforward calculation of 2D electronic spectrograms in finite molecular systems. → Importance of population time dynamics in relation to inter-site coherent coupling. - Abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems and simplified line broadening models is presented. The Fourier picture of a heterodyne detected three-pulse rephasing PE signal in the δ-pulse limit of the external field is derived in analytic form. The method includes contributions of one and two-excitonic states and allows direct calculation of Fourier PE spectrogram from corresponding Hamiltonian. As an illustration, the proposed treatment is applied to simple systems, e.g. 2-site two-level system (TLS) and n-site TLS model of photosynthetic unit. The importance of relation between Fourier picture of 3P-PE dynamics (corresponding to nonzero population time, T) and coherent inter-state coupling is emphasized.

  10. Spin-Orbit Interaction and Related Transport Phenomena in 2d Electron and Hole Systems

    Khaetskii, A.

    Spin-orbit interaction is responsible for many physical phenomena which are under intensive study currently. Here we discuss several of them. The first phenomenon is the edge spin accumulation, which appears due to spin-orbit interaction in 2D mesoscopic structures in the presence of a charge current. We consider the case of a strong spin-orbit-related splitting of the electron spectrum, i.e. a spin precession length is small compared to the mean free path l. The structure can be either in a ballistic regime (when the mean free path is the largest scale in the problem) or quasi-ballistic regime (when l is much smaller than the sample size). We show how physics of edge spin accumulation in different situations should be understood from the point of view of unitarity of boundary scattering. Using transparent method of scattering states, we are able to explain some previous puzzling theoretical results. We clarify the important role of the form of the spin-orbit Hamiltonian, the role of the boundary conditions, etc., and reveal the wrong results obtained in the field by other researchers. The relation between the edge spin density and the bulk spin current in different regimes is discussed. The detailed comparison with the existing theoretical works is presented. Besides, we consider several new transport phenomena which appear in the presence of spin-orbit interaction, for example, magnetotransport phenomena in an external classical magnetic field. In particular, new mechanism of negative magneto-resistance appears which is due to destruction of spin fluxes by the magnetic field, and which can be really pronounced in 2D systems with strong scatterers.

  11. Axial turbomachine modelling with a quasi-2-D approach. Application to gas cooled reactor transients

    Full text of publication follows: In the frame of the international forum GenIV, CEA has selected two innovative concepts of High Temperature gas cooled Reactor. The first has a fast neutron spectrum, a robust refractory fuel and a direct cycle conversion. The second is a very high temperature reactor with a thermal neutron spectrum. Both concepts make use of technology derived from High Temperature Gas Reactor. Thermal hydraulic performances are a key issue for the design. For transient conditions and decay heat removal situations, the thermal hydraulic performance must remain as high as possible. In this context, all the transient situations, the incidental and accidental scenarios must be evaluated by a validated system code able to correctly describe, in particular, the thermal-hydraulics of the whole plant. With this type of reactor a special emphasis must be laid on turbomachinery modelling. A first step was to compute a HTGR concept using the steady-state characteristics of each element of the turbomachinery with the computer code CATHARE. In a hypothetical transient event (a 10 inches cold duct break of primary loop which causes a rapid depressurization and a decrease of the core mass flow rate) the results seem of great interest (as a forced convection was maintained by the compressors during the entire transient) but not sufficiently justified in the frame of 0D modelling of turbomachinery. A more precise description of the turbomachinery has been developed based on a quasi-two dimensional approach. Although this type of flow analysis is a simplification of a complex three dimensional system, it is able to describe the behaviour of a compressor or a turbine with a better understanding than the models based on component characteristics. This approach consists in the solving of 2D radially averaged Navier-Stokes equations with the hypothesis of circumferentially uniform flow. The assumption of quasi-steady behaviour is made: source terms for the lift and

  12. Stand-alone PC-based fast readout electronics and software for 2D-gaseous detectors

    A novel readout system based on time signals processing and digitization for 2-D gaseous radiation detectors is presented. It is comprised of fast amplifiers, constant fraction discriminators, a dedicated 486 PC/AT-born time-to-digital converter and data acquisition boards and software. Its software package runs under Windows 3.1. The system allows for fast real-time data acquisition as well as for on-line and off-line data processing and image analysis. At event rates reaching 3 kHz this readout system provides an efficient and convenient tool for laboratory tests. It can operate at higher rates, exceeding 0.5 MHz under DOS. The entire system is stand-alone and does not require any additional electronics. It can operate under both external and self-triggering modes. The novel system is versatile and may be applied for the readout of a large variety of gaseous imaging detectors. Images acquired by X-ray and β imaging avalanche gas detectors equipped with this electronic system and using the software package are presented. ((orig.))

  13. Influences of quantum mechanically mixed electronic and vibrational pigment states in 2D electronic spectra of photosynthetic systems: Strong electronic coupling cases

    Fujihashi, Yuta; Ishizaki, Akihito

    2015-01-01

    In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongl...

  14. Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks.

    Güell, Aleix G; Ebejer, Neil; Snowden, Michael E; McKelvey, Kim; Macpherson, Julie V; Unwin, Patrick R

    2012-07-17

    Carbon nanotubes have attracted considerable interest for electrochemical, electrocatalytic, and sensing applications, yet there remains uncertainty concerning the intrinsic electrochemical (EC) activity. In this study, we use scanning electrochemical cell microscopy (SECCM) to determine local heterogeneous electron transfer (HET) kinetics in a random 2D network of single-walled carbon nanotubes (SWNTs) on an Si/SiO(2) substrate. The high spatial resolution of SECCM, which employs a mobile nanoscale EC cell as a probe for imaging, enables us to sample the responses of individual portions of a wide range of SWNTs within this complex arrangement. Using two redox processes, the oxidation of ferrocenylmethyl trimethylammonium and the reduction of ruthenium (III) hexaamine, we have obtained conclusive evidence for the high intrinsic EC activity of the sidewalls of the large majority of SWNTs in networks. Moreover, we show that the ends of SWNTs and the points where two SWNTs cross do not show appreciably different HET kinetics relative to the sidewall. Using finite element method modeling, we deduce standard rate constants for the two redox couples and demonstrate that HET based solely on characteristic defects in the SWNT side wall is highly unlikely. This is further confirmed by the analysis of individual line profiles taken as the SECCM probe scans over an SWNT. More generally, the studies herein demonstrate SECCM to be a powerful and versatile method for activity mapping of complex electrode materials under conditions of high mass transport, where kinetic assignments can be made with confidence. PMID:22635266

  15. Variable-range hopping in 2D quasi-1D electronic systems

    A semi-phenomenological theory of variable-range hopping (VRH) is developed for two-dimensional (2D) quasi-one-dimensional (quasi-1D) systems such as arrays of quantum wires in the Wigner crystal regime. The theory follows the phenomenology of Efros, Mott and Shklovskii allied with microscopic arguments. We first derive the Coulomb gap in the single-particle density of states, g(ε), where ε is the energy of the charge excitation. We then derive the main exponential dependence of the electron conductivity in the linear (L), i.e. σ(T) ∼ exp [-(TL/T)γL], and current in the non-linear (NL), i.e. j(E) ∼ [-(ENL/E)γNL], response regimes (E is the applied electric field). Due to the strong anisotropy of the system and its peculiar dielectric properties we show that unusual, with respect to known results, Coulomb gaps open followed by unusual VRH laws, i.e. with respect to the disorder-dependence of TL and ENL and the values of γL and γNL. (author)

  16. A New 2D-Advection-Diffusion Model Simulating Trace Gas Distributions in the Lowermost Stratosphere

    Hegglin, M. I.; Brunner, D.; Peter, T.; Wirth, V.; Fischer, H.; Hoor, P.

    2004-12-01

    Tracer distributions in the lowermost stratosphere are affected by both, transport (advective and non-advective) and in situ sources and sinks. They influence ozone photochemistry, radiative forcing, and heating budgets. In-situ measurements of long-lived species during eight measurement campaigns revealed relatively simple behavior of the tracers in the lowermost stratosphere when represented in an equivalent-latitude versus potential temperature framework. We here present a new 2D-advection-diffusion model that simulates the main transport pathways influencing the tracer distributions in the lowermost stratosphere. The model includes slow diabatic descent of aged stratospheric air and vertical and/or horizontal diffusion across the tropopause and within the lowermost stratosphere. The diffusion coefficients used in the model represent the combined effects of different processes with the potential of mixing tropospheric air into the lowermost stratosphere such as breaking Rossby and gravity waves, deep convection penetrating the tropopause, turbulent diffusion, radiatively driven upwelling etc. They were specified by matching model simulations to observed distributions of long-lived trace gases such as CO and N2O obtained during the project SPURT. The seasonally conducted campaigns allow us to study the seasonal dependency of the diffusion coefficients. Despite its simplicity the model yields a surprisingly good description of the small scale features of the measurements and in particular of the observed tracer gradients at the tropopause. The correlation coefficients between modeled and measured trace gas distributions were up to 0.95. Moreover, mixing across isentropes appears to be more important than mixing across surfaces of constant equivalent latitude (or PV). With the aid of the model, the distribution of the fraction of tropospheric air in the lowermost stratosphere can be determined.

  17. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    Fujihashi, Yuta; Ishizaki, Akihito

    2015-01-01

    Recently, nuclear vibrational contribution signatures in 2D electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the e...

  18. Magneto-transport characteristics of a 2D electron system driven to negative magneto-conductivity by microwave photoexcitation

    Mani, R. G.; Kriisa, A.

    2013-01-01

    Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking-property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible fo...

  19. Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with Terahertz Cavity Photons

    Zhang, Qi; Li, Xinwei; Reno, John L; Pan, Wei; Watson, John D; Manfra, Michael J; Kono, Junichiro

    2016-01-01

    Nonperturbative coupling of light with condensed matter in an optical cavity is expected to reveal a host of coherent many-body phenomena and states. In addition, strong coherent light-matter interaction in a solid-state environment is of great interest to emerging quantum-based technologies. However, creating a system that combines a long electronic coherence time, a large dipole moment, and a high cavity quality ($Q$) factor has been a challenging goal. Here, we report collective ultrastrong light-matter coupling in an ultrahigh-mobility two-dimensional electron gas in a high-$Q$ terahertz photonic-crystal cavity in a quantizing magnetic field, demonstrating a cooperativity of $\\sim$360. The splitting of cyclotron resonance (CR) into the lower and upper polariton branches exhibited a $\\sqrt{n_\\mathrm{e}}$-dependence on the electron density ($n_\\mathrm{e}$), a hallmark of collective vacuum Rabi splitting. Furthermore, a small but definite blue shift was observed for the polariton frequencies due to the norma...

  20. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    Fujihashi, Yuta; Ishizaki, Akihito, E-mail: ishizaki@ims.ac.jp [Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585 (Japan); Fleming, Graham R. [Department of Chemistry, University of California, Berkeley and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2015-06-07

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  1. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications

  2. A Bioactive Carbon Nanotube-Based Ink for Printing 2D and 3D Flexible Electronics.

    Shin, Su Ryon; Farzad, Raziyeh; Tamayol, Ali; Manoharan, Vijayan; Mostafalu, Pooria; Zhang, Yu Shrike; Akbari, Mohsen; Jung, Sung Mi; Kim, Duckjin; Comotto, Mattia; Annabi, Nasim; Al-Hazmi, Faten Ebrahim; Dokmeci, Mehmet R; Khademhosseini, Ali

    2016-05-01

    The development of electrically conductive carbon nanotube-based inks is reported. Using these inks, 2D and 3D structures are printed on various flexible substrates such as paper, hydrogels, and elastomers. The printed patterns have mechanical and electrical properties that make them beneficial for various biological applications. PMID:26915715

  3. Electronic structure of disordered CuPd alloys by positron-annihilation 2D-ACAR

    We report 2D-ACAR experiments and KKR CPA calculations on alpha-phase single-crystal Cu/sub 1-x/Pd/sub x/ in the range x ≤ 0.25. The flattening of the Fermi surface near [110] with increasing x predicted by theory is confirmed by our experimental results. 16 refs., 2 figs

  4. Differences in round wood measurements using electronic 2D and 3D systems and standard manual method

    Karel Janák

    2007-11-01

    Full Text Available This paper describes the use of electronic scanning systems for round wood in the Czech Republic. It analyses the two most wide-spread systems (2D and 3D, compares the values of diameters and volumes measured by these systems with the results of measurements using the Huber method and evaluates differences. The volume of the logs determined by the 2D system was 0.4 – 0.5% higher than the volume determined by manual comparative measurement. The deviation is in the range of possible measuring accuracy. The log volume determined by the 3D system was 2.5 – 5.5% lower than by careful manual measurement. The log volumes stated in the delivery bills arevery rough and they cannot be used to assess the accuracy of electronic measurement systems. The study briefly outlines the present state and trends of the electronic reception of logs in the Czech Republic.

  5. Sharp increase of the effective mass near the critical density in a metallic 2D electron system

    Shashkin, A. A.; Kravchenko, S. V.; Dolgopolov, V. T.; Klapwijk, T. M.

    2001-01-01

    We find that at intermediate temperatures, the metallic temperature dependence of the conductivity \\sigma(T) of 2D electrons in silicon is described well by a recent interaction-based theory of Zala et al. (Phys. Rev. B 64, 214204 (2001)). The tendency of the slope d\\sigma/dT to diverge near the critical electron density is in agreement with the previously suggested ferromagnetic instability in this electron system. Unexpectedly, it is found to originate from the sharp enhancement of the effe...

  6. Methods for Solving Gas Damping Problems in Perforated Microstructures Using a 2D Finite-Element Solver

    Peter Raback

    2007-06-01

    Full Text Available We present a straightforward method to solve gas damping problems for perfo-rated structures in two dimensions (2D utilising a Perforation Profile Reynolds (PPR solver.The PPR equation is an extended Reynolds equation that includes additional terms modellingthe leakage flow through the perforations, and variable diffusivity and compressibility pro-files. The solution method consists of two phases: 1 determination of the specific admittanceprofile and relative diffusivity (and relative compressibility profiles due to the perforation,and 2 solution of the PPR equation with a FEM solver in 2D. Rarefied gas corrections inthe slip-flow region are also included. Analytic profiles for circular and square holes withslip conditions are presented in the paper. To verify the method, square perforated damperswith 16 – 64 holes were simulated with a three-dimensional (3D Navier-Stokes solver, a ho-mogenised extended Reynolds solver, and a 2D PPR solver. Cases for both translational (innormal to the surfaces and torsional motion were simulated. The presented method extendsthe region of accurate simulation of perforated structures to cases where the homogenisationmethod is inaccurate and the full 3D Navier-Stokes simulation is too time-consuming.

  7. Self-consistent theory of phonon renormalization and electron-phonon coupling near a 2D Kohn singularity

    Dolgov, O. V.; Andersen, O.K.; Mazin, I. I.

    2007-01-01

    We show that the usual expression for evaluating electron-phonon coupling and the phonon linewidth in 2D metals with a cylindrical Fermi surface cannot be applied near the wave vector corresponding to the Kohn singularity. Instead, the Dyson equation for phonons has to be solved self-consistently. If a self-consistent procedure is properly followed, there is no divergency in either the coupling constant or the phonon linewidth near the offending wave vectors, in contrast to the standard expre...

  8. 2D models of gas flow and ice grain acceleration in Enceladus' vents using DSMC methods

    Tucker, Orenthal J.; Combi, Michael R.; Tenishev, Valeriy M.

    2015-09-01

    The gas distribution of the Enceladus water vapor plume and the terminal speeds of ejected ice grains are physically linked to its subsurface fissures and vents. It is estimated that the gas exits the fissures with speeds of ∼300-1000 m/s, while the micron-sized grains are ejected with speeds comparable to the escape speed (Schmidt, J. et al. [2008]. Nature 451, 685-688). We investigated the effects of isolated axisymmetric vent geometries on subsurface gas distributions, and in turn, the effects of gas drag on grain acceleration. Subsurface gas flows were modeled using a collision-limiter Direct Simulation Monte Carlo (DSMC) technique in order to consider a broad range of flow regimes (Bird, G. [1994]. Molecular Gas Dynamics and the Direct Simulation of Gas Flows. Oxford University Press, Oxford; Titov, E.V. et al. [2008]. J. Propul. Power 24(2), 311-321). The resulting DSMC gas distributions were used to determine the drag force for the integration of ice grain trajectories in a test particle model. Simulations were performed for diffuse flows in wide channels (Reynolds number ∼10-250) and dense flows in narrow tubular channels (Reynolds number ∼106). We compared gas properties like bulk speed and temperature, and the terminal grain speeds obtained at the vent exit with inferred values for the plume from Cassini data. In the simulations of wide fissures with dimensions similar to that of the Tiger Stripes the resulting subsurface gas densities of ∼1014-1020 m-3 were not sufficient to accelerate even micron-sized ice grains to the Enceladus escape speed. In the simulations of narrow tubular vents with radii of ∼10 m, the much denser flows with number densities of 1021-1023 m-3 accelerated micron-sized grains to bulk gas speed of ∼600 m/s. Further investigations are required to understand the complex relationship between the vent geometry, gas source rate and the sizes and speeds of ejected grains.

  9. Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices

    Zhou, Si; Zhao, Jijun

    2016-04-01

    Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ~1000 cm2 V-1 s-1 even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor

  10. Layer-by-Layer Assembled 2D Montmorillonite Dielectrics for Solution-Processed Electronics.

    Zhu, Jian; Liu, Xiaolong; Geier, Michael L; McMorrow, Julian J; Jariwala, Deep; Beck, Megan E; Huang, Wei; Marks, Tobin J; Hersam, Mark C

    2016-01-01

    Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of ≈600 nF cm(-2) and low leakage currents down to 6 × 10(-9) A cm(-2) that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and n-type indium gallium zinc oxide field-effect transistors. PMID:26514248

  11. Autodetachment dynamics of acrylonitrile anion revealed by 2D electron impact spectra

    We have measured the elastic and vibrationally inelastic differential cross sections in acrylonitrile at the scattering angle of 135°. We have found out that the bands at 2.9 and 4.4 eV are shape resonances, while sharp structures in the region 0 -0.5 eV are either boomerang structure of a shape resonance or vibrational Feshbach resonances. We gain detailed view of the autodetachment dynamics from a 2D spectrum where cross section is plotted against the incident energy and the energy loss.

  12. MITL: A 2-D code to investigate electron flow through non-uniform field region of magnetically insulated transmission lines

    Self-magnetically insulated, high voltage transmission lines are used in inertial confinement fusion particle accelerators to transmit power from the vacuum insulator to the diode. Injection and output convoluted sections pose special problems in establishing the desired electron flow pattern needed to maintain high overall efficiency. A time independent, 2-D numerical code for planar or triplate geometries calculates the motion of a test electron through the tapered input or output convolutes. The 1-D parapotential model is assumed to be appropriate at each position and the magnetic field and potential distribution are calculated in the vicinity of the particle. The electric field is then calculated from Gauss's Law, and the electron motion is calculated relativistically. The results show that the electron canonical momentum in the direction of flow change as the electron passes through a convoluted geometry

  13. Beyond Graphene: Electronic and Mechanical Properties of Defective 2-D Materials

    Terrones, Humberto

    One of the challenges in the production of 2-D materials is the synthesis of defect free systems which can achieve the desired properties for novel applications. However, the reality so far indicates that we need to deal with defective systems and understand their main features in order to perform defect engineering in such a way that we can engineer a new material. In this talk I discuss first, the introduction of defects in a hierarchic way starting from 2-D graphene to form giant Schwarzites or graphene foams, which also can exhibit further defects, thus we can have several levels of defectiveness. In this context, it will be shown that giant Schwarzites, depending on their symmetry, can exhibit Dirac-Fermion behavior and further, possess protected topological states as shown by other authors. Regarding the mechanical properties of these systems, it is possible to tune the Poisson Ratio by the addition of defects, thus shedding light to the explanation of the almost zero Poisson ratios in experimentally obtained graphene foams. Second, the idea of Haeckelites, a planar sp2 graphene-like structure with heptagons and pentagons, can be extended to transition metal dichalcogenides (TMDs) with square and octagonal-like defects, finding semi-metallic behaviors with Dirac-Fermions, and even topological insulating properties. National Science Foundation (EFRI-1433311).

  14. Electron Momentum Distribution Mapping of Trans-Stilbene Projected to [101] by Positron 2D-ACAR

    Selvakumar, S.; Sivaji, K.; Smith, S. V.

    Electron momentum distribution (EMD) on trans-stilbene single crystal projected along [101] direction has been studied by using positron two dimensional -angular correlation of annihilation radiation (2D-ACAR). The projected EMD is explained with respect to the molecular arrangement in the plane. The EMD features reflected the delocalized electronic states in [101] direction. The results of EMD mapping did not show a characteristic ellipsoidal distribution at lower momentum region (LMR) as observed in trans-stilbene projected to [010] direction at room temperature. The LMR region exhibits a hexagonal contour projected to [101] direction.

  15. 2-D spectroscopy and modeling of the biconical ionized gas in NGC 4388

    Ciroi, S.; Contini, M.; Rafanelli, P.; Richter, G. M.

    2003-01-01

    We present recent results from spectroscopic data and modeling of the biconical ionized gas in the Seyfert-2 galaxy NGC 4388. A field of ~2.6 x 2.4 kpc centered on the nucleus has been observed by means of the modern technique of integral field spectroscopy. The analysis of more than two hundred spectra allowed to study the physical characteristics of the gas in the surroundings of the active nucleus. The South-West ionization cone, revealed by the [O III]5007/H-beta excitation map, shows hig...

  16. 2D Spin-Dependent Diffraction of Electrons From Periodical Chains of Nanomagnets

    Teshome Senbeta

    2012-03-01

    Full Text Available The scattering of the unpolarized beams of electrons by nanomagnets in the vicinity of some scattering angles leads to complete spin polarized electrons. This result is obtained with the help of the perturbation theory. The dipole-dipole interaction between the magnetic moment of the nanomagnet and the magnetic moment of electron is treated as perturbation. This interaction is not spherically symmetric. Rather it depends on the electron spin variables. It in turn results in spinor character of the scattering amplitudes. Due to the smallness of the magnetic interactions, the scattering length of this process is very small to be proved experimentally. To enhance the relevant scattering lengths, we considered the diffraction of unpolarized beams of electrons by linear chains of nanomagnets. By tuning the distance between the scatterers it is possible to obtain the diffraction maximum of the scattered electrons at scattering angles which corresponds to complete spin polarization of electrons. It is shown that the total differential scattering length is proportional to N2 (N is a number of scatterers. Even small number of nanomagnets in the chain helps to obtain experimentally visible enhancement of spin polarization of the scattered electrons.

  17. 2-D PIC simulation on electron sheath formation in magnetized plasmas

    In order to analyze electron sheath formation we performed two dimensional PIC (Particle In Cell) simulations in magnetized plasmas. We investigated the influence of the probe geometry on the electron sheath formation in terms of the aspect ratio of the plane probe. The dependence of the magnetic field and voltage bias of the probe on the electron sheath were also taken into consideration. The sheath thickness was also analyzed to compare with the theoretical formula described by the Child Langmuir (CL) law and the experimental observations. We found that alteration of the plane probe geometry from rectangular to square decreased sheath thickness, resulting in a close to cylindrical CL sheath, rather than a planar one. These results demonstrate that the behavior of electrons surrounding the probe is directly affected by the geometry of the probe. Further, it is found that the sheath thickness is determined by the ratio between the probe width and the Larmor radius of the electron. (author)

  18. Many-body effects in electron spin resonance in 2D systems with Rashba spin-orbit interaction

    We report effects of electron–electron (e–e) interaction on electron spin resonance (ESR) in two-dimensional (2D) systems with Rashba spin–orbit interaction (SOI). Using the Hartree–Fock approximation, we demonstrate that Rashba SOI results in non-zero many-body corrections to the ESR energy. We discover that e–e interaction in 2D systems with SOI can not only enhance the ESR energy but also lead to the ESR energy reduction. The magnitude of this effect exhibits remarkable features in a wide range of parameters relevant to experiment: it is found to be rather sensitive to the sign of g-factor and the filling factor of Landau levels ν. We derive analytical expressions for many-body corrections to ESR energy and energy dispersion of spin wave excitations for the case of ν⩽2. We have found out that e–e interaction does not affect the ESR energy in the case of filling of the lowest Landau level (ν⩽1) in 2D systems with positive g-factors even at arbitrarily large values of Rashba constant. The many-body renormalization of ESR energy in the case of fractional Quantum Hall effect is also discussed. (papers)

  19. Quantum-dot systems prepared by 2D organization of nanoclusters preformed in the gas phase on functionalized substrates

    The low-energy cluster beam deposition (LECBD) technique is used to deposit gold nanoclusters preformed in the gas phase on functionalized graphite substrates (highly oriented pyrolitic graphite (HOPG)), to prepare 2D-organized arrays of cluster assembled dots. Functionalized HOPG substrates are obtained using the focused ion beam (FIB) nanoengraving technique to pattern 2D-organized arrays of defects (nanoholes, nanobumps) which act as traps for the diffusing clusters. Depending on the deposition conditions (nature, size and fluence of the deposited clusters) and the functionalized substrates (nature and size of the FIB-induced defects, geometry of the 2D array of defects and temperature during deposition) high-quality quantum-dot arrays can be obtained with well controlled and reproducible morphologies. Kinetic Monte Carlo simulations of the cluster deposition experiments on functionalized substrates allow us to obtain quite good fits of the experimental images performed by tapping mode atomic force microscopy (TMAFM), leading to systematic investigations of the best conditions to realize high-quality quantum dots systems. This combined top-down-bottom-up approach (LECBD-FIB) seems a promising method for preparing high-integration-density devices (∼Tbit cm-2) well suited for future applications to data storage, nanoelectronics, nano-optics, nanomagnetic systems

  20. Energy of the quasi-free electron in H2, D2, and O2: Probing intermolecular potentials within the local Wigner-Seitz model

    We present for the first time the quasi-free electron energy V0(ρ) for H2, D2, and O2 from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V0(ρ) accurately in strongly absorbing fluids (e.g., O2) and fluids with extremely low critical temperatures (e.g., H2 and D2). We also show that the isotropic local Wigner-Seitz model for V0(ρ) — when coupled with thermodynamic data for the fluid — can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths

  1. Secondary electron emission from solid HD and a solid H2-D2 mixture

    Sørensen, H.; Børgesen, P.; Hao-Ming, Chen;

    1983-01-01

    Secondary electron emission from solid HD and a solid 0.6 H2 + 0.4 D2 mixture has been studied for electron and hydrogen ion bombardment at primary energies from 0.5 to 3 keV and 2 to 10 keV/amu, respectively. The yield for solid HD is well explained by a simple stoichiometric model of the low......-energy stopping power for the internal secondaries. The secondary electron yield from the mixture is somewhat larger than the expected value, but lies between the values for pure solid H2 and D2. The secondary electron emission coefficient for solid tritium may be determined from a linear extrapolation of the...

  2. Enhancement of low-energy electron emission in 2D radioactive films

    Pronschinske, A.; Pedevilla, P.; Murphy, C. J.; Lewis, E. A.; Lucci, F. R.; Brown, G.; Pappas, G.; Michaelides, A.; Sykes, E. C.

    2015-01-01

    High-energy radiation has been used for decades; however, the role of low-energy electrons created during irradiation has only recently begun to be appreciated. Low-energy electrons are the most important component of radiation damage in biological environments because they have subcellular ranges, interact destructively with chemical bonds, and are the most abundant product of ionizing particles in tissue. However, methods for generating them locally without external stimulation do not exist...

  3. Acoustic 2D full waveform inversion to solve gas cloud challenges

    Srichand Prajapati

    2015-09-01

    Full Text Available The existing conventional inversion algorithm does not provide satisfactory results due to the complexity of propagated wavefield though the gas cloud. Acoustic full waveform inversion has been developed and applied to a realistic synthetic offshore shallow gas cloud feature with Student-t approach, with and without simultaneous sources encoding. As a modeling operator, we implemented the grid based finite-difference method in frequency domain using second order elastic wave equation. Jacobin operator and its adjoint provide a necessary platform for solving full waveform inversion problem in a reduced Hessian matrix. We invert gas cloud model in 5 frequency band selected from 1 to 12 Hz, each band contains 3 frequencies. The inversion results are highly sensitive to the misfit. The model allows better convergence and recovery of amplitude losses. This approach gives better resolution then the existing least-squares approach. In this paper, we implement the full waveform inversion for low frequency model with minimum number of iteration providing a better resolution of inversion results.

  4. Angle-resolved 2D imaging of electron emission processes in atoms and molecules

    A variety of electron emission processes have been studied in detail for both atomic and molecular systems, using a highly efficient experimental system comprising two time-of-flight (TOF) rotatable electron energy analyzers and a 3rd generation synchrotron light source. Two examples are used here to illustrate the obtained results. Firstly, electron emissions in the HCL molecule have been mapped over a 14 eV wide photon energy range over the Cl 2p ionization threshold. Particular attention is paid to the dissociative core-excited states, for which the Auger electron emission shows photon energy dependent features. Also, the evolution of resonant Auger to the normal Auger decay distorted by post-collision interaction has been observed and the resonating behavior of the valence photoelectron lines studied. Secondly, an atomic system, neon, in which excitation of doubly excited states and their subsequent decay to various accessible ionic states has been studied. Since these processes only occurs via inter-electron correlations, the many body dynamics of an atom can be probed, revealing relativistic effects, surprising in such a light atom. Angular distribution of the decay of the resonances to the parity unfavored continuum exhibits significant deviation from the LS coupling predictions

  5. Oxide 2D electron gases as a route for high carrier densities on (001) Si

    Kornblum, Lior; Jin, Eric N.; Kumah, Divine P.; Walker, Fred J. [Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut 06511 (United States); Department of Applied Physics, Yale University, New Haven, Connecticut 06511 (United States); Ernst, Alexis T.; Broadbridge, Christine C. [Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut 06511 (United States); Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, Connecticut 06515 (United States); Ahn, Charles H. [Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut 06511 (United States); Department of Applied Physics, Yale University, New Haven, Connecticut 06511 (United States); Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511 (United States)

    2015-05-18

    Two dimensional electron gases (2DEGs) formed at the interfaces of oxide heterostructures draw considerable interest owing to their unique physics and potential applications. Growing such heterostructures on conventional semiconductors has the potential to integrate their functionality with semiconductor device technology. We demonstrate 2DEGs on a conventional semiconductor by growing GdTiO{sub 3}-SrTiO{sub 3} on silicon. Structural analysis confirms the epitaxial growth of heterostructures with abrupt interfaces and a high degree of crystallinity. Transport measurements show the conduction to be an interface effect, ∼9 × 10{sup 13} cm{sup −2} electrons per interface. Good agreement is demonstrated between the electronic behavior of structures grown on Si and on an oxide substrate, validating the robustness of this approach to bridge between lab-scale samples to a scalable, technologically relevant materials system.

  6. Oxide 2D electron gases as a route for high carrier densities on (001) Si

    Two dimensional electron gases (2DEGs) formed at the interfaces of oxide heterostructures draw considerable interest owing to their unique physics and potential applications. Growing such heterostructures on conventional semiconductors has the potential to integrate their functionality with semiconductor device technology. We demonstrate 2DEGs on a conventional semiconductor by growing GdTiO3-SrTiO3 on silicon. Structural analysis confirms the epitaxial growth of heterostructures with abrupt interfaces and a high degree of crystallinity. Transport measurements show the conduction to be an interface effect, ∼9 × 1013 cm−2 electrons per interface. Good agreement is demonstrated between the electronic behavior of structures grown on Si and on an oxide substrate, validating the robustness of this approach to bridge between lab-scale samples to a scalable, technologically relevant materials system

  7. Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging

    Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.

  8. Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging

    Tobias, Ben [University of California, Davis; Classen, I.G.J. [FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands; Domier, C. W. [University of California, Davis; Heidbrink, W. [University of California, Irvine; Luhmann, N.C. [University of California, Davis; Nazikian, Raffi [Princeton Plasma Physics Laboratory (PPPL); Park, H.K. [Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea; Spong, Donald A [ORNL; Van Zeeland, Michael [General Atomics

    2011-01-01

    Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.

  9. 2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures

    Bourdon, Anne

    2015-09-01

    Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N2 discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N2 in the He-N2 mixture. In particular, as the amount of N2 admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about 0 . 1 % of N2 and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves

  10. Pion transfer from hydrogen to deuterium in H2+D2 gas mixtures

    The transfer of negative pions from pionic hydrogen to deuterium has been investigated in gas mixtures of H2 and D2 as a function of the D2 concentration. The concentration dependence of the transfer rate was fitted using a phenomenological model with two parameters. For C → ∞ (32±3)% of the pions undergo transfer. The fitted parameters reflect the ratio of pion capture to pion transfer in collisions of pionic hydrogen with protons or deuterons. No pressure dependence for pion transfer was found. (Author) 33 refs., 3 tabs., 7 figs

  11. Electron Compton defect observed in He, H2, D2, N2, and Ne profiles

    A high-energy electron-impact spectroscopy (HEEIS) apparatus has been constructed for high-precision Compton-scattering experiments. Electron-Compton-scattering experiments are performed by crossing a beam of high energy, but nonrelativistic, electrons with a beam of atoms or molecules and measuring the energy-loss spectrum of the scattered electrons over a range of scattering angles. The improvements of design and technique, the method of data analysis, and the theory used to convert cross sections to Compton profiles are discussed fully. It was found that the energy-loss spectra taken over a range of scattering angles do not reduce by means of the binary-encounter approximation (impulse approximation) to Compton profiles in agreement with theory. This disagreement is most apparent in a shift of the experimental Compton peak: the Compton defect: from the peak predicted by the binary-encounter theory. The Compton defect has been studied in detail for momentum transfers from 1.5--12 a.u. for both He and H2. Defect measurements for D2, N2, and Ne have also been made and it was found that the N2 and Ne defects were opposite in direction from the He and H2 defects. The D2 defect was identical to that for H2. The electron Compton defect is discussed in relation to other recent defect measurements using x-ray and (e,2e) techniques as well as recent theoretical results. An evaluation of the theory used to convert cross sections to Compton profiles is presented and, on the basis of the defect measurements, it is suggested that, even when the binary-encounter conditions have been attained at large momentum transfers, the binary-encounter theory breaks down in the high accuracy (1%) limit. An explanation for this breakdown is given and recent theories, which at least qualitatively account for the Compton defect, are discussed

  12. A Fast Parallel Algorithm for Selected Inversion of Structured Sparse Matrices with Application to 2D Electronic Structure Calculations

    Lin, Lin; Yang, Chao; Lu, Jiangfeng; Ying, Lexing; E, Weinan

    2009-09-25

    We present an efficient parallel algorithm and its implementation for computing the diagonal of $H^-1$ where $H$ is a 2D Kohn-Sham Hamiltonian discretized on a rectangular domain using a standard second order finite difference scheme. This type of calculation can be used to obtain an accurate approximation to the diagonal of a Fermi-Dirac function of $H$ through a recently developed pole-expansion technique \\cite{LinLuYingE2009}. The diagonal elements are needed in electronic structure calculations for quantum mechanical systems \\citeHohenbergKohn1964, KohnSham 1965,DreizlerGross1990. We show how elimination tree is used to organize the parallel computation and how synchronization overhead is reduced by passing data level by level along this tree using the technique of local buffers and relative indices. We analyze the performance of our implementation by examining its load balance and communication overhead. We show that our implementation exhibits an excellent weak scaling on a large-scale high performance distributed parallel machine. When compared with standard approach for evaluating the diagonal a Fermi-Dirac function of a Kohn-Sham Hamiltonian associated a 2D electron quantum dot, the new pole-expansion technique that uses our algorithm to compute the diagonal of $(H-z_i I)^-1$ for a small number of poles $z_i$ is much faster, especially when the quantum dot contains many electrons.

  13. A Fast Parallel Algorithm for Selected Inversion of Structured Sparse Matrices with Application to 2D Electronic Structure Calculations

    We present an efficient parallel algorithm and its implementation for computing the diagonal of H-1 where H is a 2D Kohn-Sham Hamiltonian discretized on a rectangular domain using a standard second order finite difference scheme. This type of calculation can be used to obtain an accurate approximation to the diagonal of a Fermi-Dirac function of H through a recently developed pole-expansion technique LinLuYingE2009. The diagonal elements are needed in electronic structure calculations for quantum mechanical systems HohenbergKohn1964, KohnSham 1965,DreizlerGross1990. We show how elimination tree is used to organize the parallel computation and how synchronization overhead is reduced by passing data level by level along this tree using the technique of local buffers and relative indices. We analyze the performance of our implementation by examining its load balance and communication overhead. We show that our implementation exhibits an excellent weak scaling on a large-scale high performance distributed parallel machine. When compared with standard approach for evaluating the diagonal a Fermi-Dirac function of a Kohn-Sham Hamiltonian associated a 2D electron quantum dot, the new pole-expansion technique that uses our algorithm to compute the diagonal of (H-zi I)-1 for a small number of poles zi is much faster, especially when the quantum dot contains many electrons.

  14. Electron collisions in gas switches

    Many technologies rely on the conduction/insulation properties of gaseous matter for their successful operation. Many others (e.g., pulsed power technologies) rely on the rapid change (switching or modulation) of the properties of gaseous matter from an insulator to a conductor and vice versa. Studies of electron collision processes in gases aided the development of pulsed power gas switches, and in this paper we shall briefly illustrate the kind of knowledge on electron collision processes which is needed to optimize the performance of such switching devices. To this end, we shall refer to three types of gas switches: spark gap closing, self-sustained diffuse discharge closing, and externally-sustained diffuse discharge opening. 24 refs., 15 figs., 2 tabs

  15. Electron-positron momentum density distribution of Gd from 2D ACAR data via maximum entropy and Cormack's methods

    A successful application of the maximum entropy method (MEM) to the reconstruction of electron-positron momentum density distribution in gadolinium out of the experimental of 2D ACAR data is presented. Formally, the algorithm used was prepared for two-dimensional reconstructions from line integrals. For the first time the results of MEM, applied to such data, are compared in detail with the ones obtained by means of Cormack's method. It is also shown how the experimental uncertainties may influence the results of the latter analysis. Preliminary calculations, using WIEN2k code, of band structure and Fermi surface have been done as well. (orig.)

  16. Electron-positron momentum density distribution of Gd from 2D ACAR data via Maximum Entropy and Cormack's methods

    Pylak, M.; Kontrym-Sznajd, G.; Dobrzyński, L.

    2011-08-01

    A successful application of the Maximum Entropy Method (MEM) to the reconstruction of electron-positron momentum density distribution in gadolinium out of the experimental of 2D ACAR data is presented. Formally, the algorithm used was prepared for two-dimensional reconstructions from line integrals. For the first time the results of MEM, applied to such data, are compared in detail with the ones obtained by means of Cormack's method. It is also shown how the experimental uncertainties may influence the results of the latter analysis. Preliminary calculations, using WIEN2k code, of band structure and Fermi surface have been done as well.

  17. Parallel FE Electron-Photon Transport Analysis on 2-D Unstructured Mesh

    A novel solution method has been developed to solve the coupled electron-photon transport problem on an unstructured triangular mesh. Instead of tackling the first-order form of the linear Boltzmann equation, this approach is based on the second-order form in conjunction with the conventional multi-group discrete-ordinates approximation. The highly forward-peaked electron scattering is modeled with a multigroup Legendre expansion derived from the Goudsmit-Saunderson theory. The finite element method is used to treat the spatial dependence. The solution method is unique in that the space-direction dependence is solved simultaneously, eliminating the need for the conventional inner iterations, a method that is well suited for massively parallel computers

  18. Terahertz Probes of Transient Conducting and Insulating Phases in Quasi-2D Electron-hole Gases

    We employ ultrafast terahertz (THz) pulses to study the dynamical interplay of optically-induced excitons and unbound electron-hole pairs in GaAs/AlGaAs quantum wells. A distinct low-energy oscillator appears upon resonant excitation of heavy-hole excitons, linked to transitions between their internal degrees of freedom. Time resolving changes in the THz conductivity, we can observe dynamical transitions between conducting and insulating phases as excitons form or ionize on ultrashort timescales

  19. Electronic structure effects on stability and quantum conductance in 2D gold nanowires

    In this study, we have investigated the stability and conductivity of unsupported, two-dimensional infinite gold nanowires using ab initio density functional theory (DFT). Two-dimensional ribbon-like nanowires with 1–5 rows of gold atoms in the non-periodic direction and with different possible structures have been considered. The nanowires with >2 rows of atoms exhibit dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires, the parallelogram motif is the most stable. A comparison between parallelogram- and rectangular-shaped nanowires of increasing width indicates that zero thickness (111) oriented wires have a higher stability over (100). A detailed analysis of the electronic structure, reveals that the (111) oriented structures show increased delocalization of s and p electrons in addition to a stronger delocalization of the d electrons and hence are the most stable. The density of states show that the nanowires are metallic and conducting except for the double zigzag structure, which is semiconducting. Conductance calculations show transmission for a wide range of energies in all the stable nanowires with more than two rows of atoms. The conductance channels are not purely s and have strong contributions from the d levels, and weak contributions from the p levels.

  20. Stability and electronic properties of SiGe-based 2D layered structures

    The structural and electronic properties of the in-plane hybrids consisting of siligene (SiGe), and its derivatives in both mono and bilayer forms are investigated within density functional theory. Among several pristine and hydrogenated configurations, the so-called chair conformation is energetically favorable for monolayers. On the other hand, the bilayer siligane (HSiGeH) prefers AB-stacked chair conformation and bilayer siligone (HSiGe) prefers AA-stacked buckled conformation. In SiGe, the Dirac-cone character is predicted to be retained. HSiGe is a magnetic semiconductor with a band gap of ∼0.6 eV. The electronic properties show tunability under mechanical strain and transverse electric field; (i) the energy gap opens up in the SiGe bilayer, (ii) a direct-to-indirect gap transition is predicted by the applied strain in the HSiGeH bilayer, and (iii) a semiconductor-to-metal transition is predicted for HSiGe and HSiGeH bilayers under the application of strain and electric field, thus suggesting SiGe and its derivatives to be a potential candidate for electronic devices at nanoscale. (paper)

  1. Tunable Plasmonic Reflection by Bound 1D Electron States in a 2D Dirac Metal

    Jiang, B.-Y.; Ni, G. X.; Pan, C.; Fei, Z.; Cheng, B.; Lau, C. N.; Bockrath, M.; Basov, D. N.; Fogler, M. M.

    2016-08-01

    We show that the surface plasmons of a two-dimensional Dirac metal such as graphene can be reflected by linelike perturbations hosting one-dimensional electron states. The reflection originates from a strong enhancement of the local optical conductivity caused by optical transitions involving these bound states. We propose that the bound states can be systematically created, controlled, and liquidated by an ultranarrow electrostatic gate. Using infrared nanoimaging, we obtain experimental evidence for the locally enhanced conductivity of graphene induced by a carbon nanotube gate, which supports this theoretical concept.

  2. Comparisons between tokamak fueling of gas puffing and supersonic molecular beam injection in 2D simulations

    Plasma fueling with high efficiency and deep injection is very important to enable fusion power performance requirements. It is a powerful and efficient way to study neutral transport dynamics and find methods of improving the fueling performance by doing large scale simulations. Two basic fueling methods, gas puffing (GP) and supersonic molecular beam injection (SMBI), are simulated and compared in realistic divertor geometry of the HL-2A tokamak with a newly developed module, named trans-neut, within the framework of BOUT++ boundary plasma turbulence code [Z. H. Wang et al., Nucl. Fusion 54, 043019 (2014)]. The physical model includes plasma density, heat and momentum transport equations along with neutral density, and momentum transport equations. Transport dynamics and profile evolutions of both plasma and neutrals are simulated and compared between GP and SMBI in both poloidal and radial directions, which are quite different from one and the other. It finds that the neutrals can penetrate about four centimeters inside the last closed (magnetic) flux surface during SMBI, while they are all deposited outside of the LCF during GP. It is the radial convection and larger inflowing flux which lead to the deeper penetration depth of SMBI and higher fueling efficiency compared to GP

  3. Return current 2D-mapping of short-pulse relativistic electron beams propagating in gases

    A simple model for examining the effect of rotation on electron beam ''Hose'' instabilities is presented. Using a rigid beam approximation, it is found that the equilibrium rotation of an electron beam will couple to unstable displacements. The coupling arises from a -Y x ω /sub R/ term appearing in the force equation where Y is the displacement vector and ω /sub R/ is the rotation frequency of the beam. This term can be found from either single particle motion or cold-fluid hydro equations. The effect on hose instabilities is similar to a parallel B field and is stabilizing. In the case of real W, growth in z is reduced by 18% from the non-rotating beam case, for ω /sub R/ = ω /sub lb/ where ω /sub lb/ is the betatron frequency (the rotation frequency in the cold beam limit). Using the spread mass model of Ed Lee, finite growth rates are found for growth in /tau/ = z/c - t for real Ω = ω - kc, with most unstable modes occurring at -.61 ω /sub lb/ and 1.61 ω /sub lb/ for a cold beam. For a rotating annular beam, peak growth at - and 2.5 is seen in agreement with simulations. Comparison with experimental results is shown

  4. Applications of Ultrafast Terahertz Pulses for Intra-ExcitonicSpectroscopy of Quasi-2D Electron-Hole Gases

    Kaindl, Robert A.; Carnahan, Marc A.; Hagele, Daniel; Chemla, D.S.

    2006-09-02

    Excitons are of fundamental interest and of importance foropto-electronic applications of bulk and nano-structured semiconductors.This paper discusses the utilization of ultrafast terahertz (THz) pulsesfor the study of characteristic low-energy excitations of photoexcitedquasi 2D electron-hole (e-h) gases. Optical-pump THz-probe spectroscopyat 250-kHz repetition rate is employed to detect characteristic THzsignatures of excitons and unbound e-h pairs in GaAs quantum wells.Exciton and free-carrier densities are extracted from the data using atwo-component model. We report the detailed THz response and pairdensities for different photoexcitation energies resonant to heavy-holeexcitons, light-hole excitons, or the continuum of unbound pairs. Suchexperiments can provide quantitative insights into wavelength, time, andtemperature dependence of the low-energy response and composition ofoptically excited e-h gases in low-dimensionalsemiconductors.

  5. The gas electron multiplier (GEM)

    Bouclier, Roger; Dominik, Wojciech; Hoch, M; Labbé, J C; Million, Gilbert; Ropelewski, Leszek; Sauli, Fabio; Sharma, A

    1996-01-01

    We describe operating priciples and results obtained with a new detector component: the Gas Electrons Multiplier (GEM). Consisting of a thin composite sheet with two metal layers separated by a thin insulator, and pierced by a regular matrix of open channels, the GEM electrode, inserted on the path of electrons in a gas detector, allows to transfer the charge with an amplification factor approaching ten. Uniform response and high rate capability are demonstrated. Coupled to another device, multiwire or micro-strip chamber, the GEM electrode permit to obtain higher gains or less critical operation; separation of the sensitive (conversion) volume and the detection volume has other advantages, as a built-in delay (useful for triggering purposes) and the possibility of applying high fields on the photo-cathode of ring imaging detectors to improve efficiency. Multiple GEM grids in the same gas volume allow to obtain large amplification factors in a succession of steps, leading to the realization of an effective ga...

  6. Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes

    Monahan, Daniele M.; Whaley-Mayda, Lukas; Fleming, Graham R., E-mail: grfleming@lbl.gov [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720 (United States); Ishizaki, Akihito [Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585 (Japan)

    2015-08-14

    Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.

  7. Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes

    Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing

  8. The ceramic gas electron multiplier

    Tosson, Amir; Fleck, Ivor [Siegen University, Siegen (Germany); Collaboration: LCTPC-Deutschland-Collaboration

    2015-07-01

    The Gas Electron Multiplier (GEM) has been proven to fulfill the demands of high energy physics experiments. Effective gain and resistance to the electrical sparks are significant issues to be investigated. A new type of GEM, made out of ceramic, has been produced and results from measurements with this type of GEM are presented. Advantages of ceramic material are its very good stability versus change in temperature and its electrical properties. Using Ar-CO{sub 2}(80-20 %) gas mixture and a X-ray source, the gain of the ceramic GEMs is measured and compared with the one for CERN GEMs. These results assure the possibility of using the ceramic GEMs for high-luminosity experiments.

  9. Origin of long-lived oscillations in 2D-spectra of a quantum vibronic model: Electronic versus vibrational coherence

    Plenio, M. B.; Almeida, J.; Huelga, S. F. [Institute for Theoretical Physics, Albert-Einstein-Allee 11, University Ulm, D-89069 Ulm (Germany)

    2013-12-21

    We demonstrate that the coupling of excitonic and vibrational motion in biological complexes can provide mechanisms to explain the long-lived oscillations that have been obtained in nonlinear spectroscopic signals of different photosynthetic pigment protein complexes and we discuss the contributions of excitonic versus purely vibrational components to these oscillatory features. Considering a dimer model coupled to a structured spectral density we exemplify the fundamental aspects of the electron-phonon dynamics, and by analyzing separately the different contributions to the nonlinear signal, we show that for realistic parameter regimes purely electronic coherence is of the same order as purely vibrational coherence in the electronic ground state. Moreover, we demonstrate how the latter relies upon the excitonic interaction to manifest. These results link recently proposed microscopic, non-equilibrium mechanisms to support long lived coherence at ambient temperatures with actual experimental observations of oscillatory behaviour using 2D photon echo techniques to corroborate the fundamental importance of the interplay of electronic and vibrational degrees of freedom in the dynamics of light harvesting aggregates.

  10. First-principles method for electron-phonon coupling and electron mobility: Applications to 2D materials

    Gunst, Tue; Markussen, Troels; Stokbro, Kurt; Brandbyge, Mads

    2015-01-01

    We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene and MoS$_2$. The material properties, including the electron-phonon interaction, are calculated from first-principles. We provide a detailed description of the normalized full-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell meth...

  11. 2D fluid model analysis for the effect of 3D gas flow on a capacitively coupled plasma deposition reactor

    Kim, Ho Jun; Lee, Hae June

    2016-06-01

    The wide applicability of capacitively coupled plasma (CCP) deposition has increased the interest in developing comprehensive numerical models, but CCP imposes a tremendous computational cost when conducting a transient analysis in a three-dimensional (3D) model which reflects the real geometry of reactors. In particular, the detailed flow features of reactive gases induced by 3D geometric effects need to be considered for the precise calculation of radical distribution of reactive species. Thus, an alternative inclusive method for the numerical simulation of CCP deposition is proposed to simulate a two-dimensional (2D) CCP model based on the 3D gas flow results by simulating flow, temperature, and species fields in a 3D space at first without calculating the plasma chemistry. A numerical study of a cylindrical showerhead-electrode CCP reactor was conducted for particular cases of SiH4/NH3/N2/He gas mixture to deposit a hydrogenated silicon nitride (SiN x H y ) film. The proposed methodology produces numerical results for a 300 mm wafer deposition reactor which agree very well with the deposition rate profile measured experimentally along the wafer radius.

  12. Warm ionized gas in CALIFA early-type galaxies. 2D emission-line patterns and kinematics for 32 galaxies

    Gomes, J. M.; Papaderos, P.; Kehrig, C.; Vílchez, J. M.; Lehnert, M. D.; Sánchez, S. F.; Ziegler, B.; Breda, I.; Dos Reis, S. N.; Iglesias-Páramo, J.; Bland-Hawthorn, J.; Galbany, L.; Bomans, D. J.; Rosales-Ortega, F. F.; Cid Fernandes, R.; Walcher, C. J.; Falcón-Barroso, J.; García-Benito, R.; Márquez, I.; Del Olmo, A.; Masegosa, J.; Mollá, M.; Marino, R. A.; González Delgado, R. M.; López-Sánchez, Á. R.; Califa Collaboration

    2016-04-01

    Context. The morphological, spectroscopic, and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive, quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer an unprecedented opportunity for advancing our understanding of the wim in ETGs. Aims: This article centers on a 2D investigation of the wim component in 32 nearby (≲150 Mpc) ETGs from CALIFA, complementing a previous 1D analysis of the same sample. Methods: The analysis presented here includes Hα intensity and equivalent width (EW) maps and radial profiles, diagnostic emission-line ratios, and ionized-gas and stellar kinematics. It is supplemented by τ-ratio maps, which are a more efficient means to quantify the role of photoionization by the post-AGB stellar component than alternative mechanisms (e.g., AGN, low-level star formation). Results: Confirming and strengthening our previous conclusions, we find that ETGs span a broad continuous sequence in the properties of their wim, exemplified by two characteristic classes. The first (type i) comprises systems with a nearly constant EW(Hα) in their extranuclear component, which quantitatively agrees with (but is no proof of) the hypothesis that photoionization by the post-AGB stellar component is the main driver of extended wim emission. The second class (type ii) stands for virtually wim-evacuated ETGs with a very low (≤0.5 Å), outwardly increasing EW(Hα). These two classes appear indistinguishable from one another by their LINER-specific emission-line ratios in their extranuclear component. Here we extend the tentative classification we proposed previously by the type i+, which is assigned to a subset of type i ETGs exhibiting ongoing low-level star-forming activity in their periphery. This finding along with faint

  13. Theoretical electron-positron momentum density and 2D-ACAR positron experiments in YBa2Cu3O7

    We compare measured c-projected 2D-ACAR spectrum from an untwinned single crystal of YBa2Cu3O7-x with the corresponding band theory predictions. Many different one-dimensional sections through the spectrum are considered, together with the characteristic amplitudes and shapes of the spectral anisotropies, with a focus on identifying and delineating Fermi surface signatures in the spectra. The positron data clearly show several distinct features of the ridge Fermi surface predicted by the band theory, and give an indication of the pillbox Fermi sheet. The good agreement between theory and experiment suggests that the band theory framework based on the local density approximation (LDA) is capable of providing a substantially correct description of the momentum density and Fermiology of the normal ground state electronic structure of YBa2Cu3O7

  14. Electronic band structure and charge density wave transition in quasi-2D KMo6O17 purple bronze

    Valbuena, M. A.; Avila, J.; Vyalikh, D. V.; Guyot, H.; Laubschat, C.; Molodtsov, S. L.; Asensio, M. C.

    2008-03-01

    High resolution angle-resolved photoemission of quasi-2D KMo6O17 purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (Tc = 110 K), and down to 35 K (well below Tc). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

  15. Electronic band structure and charge density wave transition in quasi-2D KMo6O17 purple bronze

    High resolution angle-resolved photoemission of quasi-2D KMo6O17 purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (Tc = 110 K), and down to 35 K (well below Tc). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities

  16. Critical behavior of transport and magnetotransport in 2D electron system in Si in the vicinity of the metal-insulator transition

    Knyazev, D. A.; Omelyanovskii, O. E.; Pudalov, V.M.; Burmistrov, I. S.

    2006-01-01

    We report on studies of the magnetoresistance in strongly correlated 2D electron system in Si in the critical regime, in the close vicinity of the 2D metal-insulator transition. We performed self-consistent comparison of our data with solutions of two equations of the cross-over renormalization group (CRG) theory which describes temperature evolutions of the resistivity and interaction parameters for 2D electron system. We found a good agreement between the \\rho(T,B) data and the RG theory in...

  17. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Qy band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state

  18. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    Enriquez, Miriam M.; Zhang, Cheng; Tan, Howe-Siang, E-mail: howesiang@ntu.edu.sg [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 (Singapore); Akhtar, Parveen; Garab, Győző; Lambrev, Petar H., E-mail: lambrev@brc.hu [Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged (Hungary)

    2015-06-07

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Q{sub y} band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  19. 2D modeling of salt precipitation during the injection of dry CO2 in a depleted gas reservoir

    The precipitation of halite around a CO2 injection well has been studied to investigate the possible effects on well injectivity for a pilot test of CO2 injection in a depleted gas reservoir. The numerical simulations performed with the TMGAS simulator, using both 1D and 2D radial grids, show that the injection of dry supercritical CO2 vaporizes the formation brine promoting NaCl concentration and the precipitation of halite. Different behaviors are observed depending on the initial liquid saturation: when the brine has a low mobility, the evaporation front advances with limited halite precipitation and only minor effects on well injectivity. On the other hand, when the brine has sufficient mobility, the precipitation front is recharged by the brine flowing towards the wellbore, due to the capillary pressure gradient driven by the evaporation. In this case the concentrated precipitation can strongly reduce the formation permeability. These effects depend on formation properties and on the porosity-permeability relationship which describes the effects of halite precipitation on permeability reduction. In the attempt to improve the prediction of halite precipitation effects, an extension of the so-called tube-in-series model of Verma and Pruess was developed, with pore-size distribution evaluated from the measured grain-size distribution of the sandy formation considered for the execution of the pilot CO2 sequestration test

  20. Measurement of turbulent diffusivity of both gas and liquid phases in quasi-2D two-phase flow

    The turbulent diffusion process has been studied experimentally by observing a tracer plume emitted continuously from a line source in a uniform, quasi-2D two-phase flow. The test section was a vertical, relatively narrow, concentric annular channel consisting of two large pipes. Air and water were used as the working fluids, and methane and acid organge II were used as tracers for the respective phases. Measurements of local, time-averaged tracer concentrations were made by means of a sampling method and image processing for bubbly flows and churn flows, and the turbulent diffusivity, the coefficient of turbulent diffusion, was determined from the concentration distributions measured. The diffusivities for the gas and liquid phases, εDG and εDL respectively, are presented and compared with each other in this paper. When a flow is bubbly, εDG is close to or slightly smaller than εDL. In a churn flow, on the contrary, εDG is much greater than εDL. Regarding bubbly flow, a plausible model on turbulent diffusivity of the liquid phase is presented and examined by the present data. (orig.)

  1. Gold-induced nanowires on the Ge(100) surface yield a 2D and not a 1D electronic structure

    de Jong, N.; Heimbuch, R.; Eliëns, S.; Smit, S.; Frantzeskakis, E.; Caux, J.-S.; Zandvliet, H. J. W.; Golden, M. S.

    2016-06-01

    Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, one-dimensional Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D (one-dimensional) metallic states. In light of this debate, we report here a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. The high-resolution ARPES data show the low-lying Au-induced electronic states to possess a dispersion relation that depends on two orthogonal directions in k space. Comparison of the E (kx,ky) surface measured using high-resolution ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by approximately factor of two. Additionally, by pinpointing the Au-induced surface states in the first, second, and third surface Brillouin zones and analyzing their periodicity in k||, the nanowire propagation direction seen clearly in STM can be imported into the ARPES data. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (tperp). This proves that the Au-induced electron pockets possess a two-dimensional, closed Fermi surface, and this firmly places the Au/Ge(100) nanowire system outside potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with scanning tunneling spectroscopic measurements of the spatially resolved electronic structure and find that the spatially straight—wirelike—conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are rather more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D (two-dimentional) nature of the Au

  2. Increase of spin dephasing times in a 2D electron system with degree of initial spin polarization

    Stich, D.; Korn, T.; Schulz, R.; Schuh, D.; Wegscheider, W.; Schüller, C.

    2008-03-01

    We report on time-resolved Faraday/Kerr rotation measurements on a high-mobility 2D electron system. A variable initial spin polarization is created in the sample by a circularly polarized pump pulse, and the spin polarization is tracked by measuring the Faraday/Kerr rotation of a time-delayed probe pulse. By varying the pump intensity, the initial spin polarization is changed from the low-polarization limit to a polarization degree of several percent. The observed spin dephasing time increases from less than 20 ps to more than 200 ps as the initial spin polarization is increased. To exclude sample heating effects, additional measurements with constant pump intensity and variable degree of circular polarization are performed. The results confirm the theoretical prediction by Weng and Wu [Phys. Rev. B 68 (2003) 075312] that the spin dephasing strongly depends on the initial spin polarization degree. The microscopic origin for this is the Hartree-Fock term in the Coulomb interaction, which acts as an effective out-of plane magnetic field.

  3. Photoluminescence and the gallium problem for highest-mobility GaAs/AlGaAs-based 2d electron gases

    Schläpfer, F.; Dietsche, W.; Reichl, C.; Faelt, S.; Wegscheider, W.

    2016-05-01

    The quest for extremely high mobilities of 2d electron gases in MBE-grown heterostructures is hampered by the available purity of the starting materials, particularly of the gallium. Here we compare the role of different Ga lots having nominally the highest possible quality on the mobility and the photoluminescence (PL) of modulation doped single interface structures and find significant differences. A weak exciton PL reveals that the purity of the Ga is insufficient. No high mobility can be reached with such a lot with a reasonable effort. On the other hand, a strong exciton PL indicates a high initial Ga purity, allowing to reach mobilities of 15 million (single interface) or 28 million cm2/V s (doped quantum wells) in our MBE systems. We discuss possible origins of the inconsistent Ga quality. Furthermore, we compare samples grown in different MBE systems over a period of several years and find that mobility and PL are correlated if similar structures and growth procedures are used.

  4. Plasma oscillations in a layered electron gas (LEG) model revisited

    Grecu, D

    2002-01-01

    The first studies on the plasma oscillations in a layered electron gas, some of them done in our laboratory, are briefly reviewed. Through molecular beam epitaxy techniques high quality superlattices have been produced in which the carriers' motion is highly 2-D. Plasmon excitations in such systems were identified in inelastic light and Raman scattering experiments. Few further developments of the many body theory in LEG systems are presented. Few remarks on plasmons in layered superconductors and in quasi-one-dimensional conductors are given. (author)

  5. Electron spectrometer for gas-phase spectroscopy

    Bozek, J.D.; Schlachter, A.S. [Ernest Orlando Lawrence Berkeley National Lab., CA (United States)

    1997-04-01

    An electron spectrometer for high-resolution spectroscopy of gaseous samples using synchrotron radiation has been designed and constructed. The spectrometer consists of a gas cell, cylindrical electrostatic lens, spherical-sector electron energy analyzer, position-sensitive detector and associated power supplies, electronics and vacuum pumps. Details of the spectrometer design are presented together with some representative spectra.

  6. 2D Multitransient Electromagnetic Response Modeling of South China Shale Gas Earth Model Using an Approximation of Finite Difference Time Domain with Uniaxial Perfectly Matched Layer

    Olalekan Fayemi

    2016-01-01

    Full Text Available In this study, we introduced multitransient electromagnetic (MTEM method as an effective tool for shale gas exploration. We combined the uniaxial perfectly matched layer (UPML equation with the first derivative diffusion equation to solve for a finite difference time domain (FDTD UPML equation, which was discretized to form an algorithm for 3D modeling of earth impulse response and used in modeling MTEM response over 2D South China shale gas model. We started with stepwise demonstration of the UPML and the FDTD algorithm as an effective tool. Subsequently, quantitative study on the convergence of MTEM earth impulse response was performed using different grid setup over a uniform earth material. This illustrates that accurate results can be obtained for specified range of offset. Furthermore, synthetic responses were generated for a set of geological scenarios. Lastly, the FDTD algorithm was used to model the MTEM response over a 2D shale gas earth model from South China using a PRBS source. The obtained apparent resistivity section from the MTEM response showed a similar geological setup with the modeled 2D South China shale gas section. This study confirmed the competence of MTEM method as an effective tool for unconventional shale gas prospecting and exploitation.

  7. Highly brilliant synchrotron radiation operando spectromicroscopy to bridge a gap between material electronic properties and device performances of 2D atomic layers

    Si-based electronics has reached an ultimate fabrication level (22 nm design rule), which makes further progress hardly achieved. Therefore, 2D atomic layers including graphene have been extensively studied as next-generation device materials to supplement device functions which Si-based electronics cannot serve. Unfortunately, however, there is a gap between material electronic properties and device performances in the researches on 2D atomic layers. We demonstrate soft x-ray operando spectromicroscopies, photoemission electron microscopy (PEEM) and 3D scanning photoelectron microscopy (3D nano-ESCA), in SPring-8 to bridge the gap in graphene research. The complementary use of these operando spectromicroscopies enables us to probe both valence band and conduction bands of graphene channels under operation, resulting in revealing the effects of the interfaces with contact metal and oxide. The significance of the operando spectromicroscopy is now recognized, resulting in the adoption as a major research target in NEDO academic-industrial alliance project. (author)

  8. Recent Achievement of Gas Electron Multiplier

    XIA Yi-ben; WANG Lin-jun; ZHANG Ming-long; YANG Ying; ZHANG Wei-li; RUAN Jian-feng

    2004-01-01

    Gas electron multiplier (GEM) as a novel gas detector, due to it's simple structure, high performance, well compatibility etc. ,is widely used in high-energy physics, nuclear physics and other fields. In this review, the principle, recent achievements,developments and applications of GEM are mainly described.

  9. Insights into Gulf of Mexico Gas Hydrate Study Sites GC955 and WR313 from New Multicomponent and High-Resolution 2D Seismic Data

    Haines, S. S.; Hart, P. E.; Collett, T. S.; Shedd, W. W.; Frye, M.

    2014-12-01

    In 2013, the U.S. Geological Survey led a seismic acquisition expedition in the Gulf of Mexico, acquiring multicomponent data and high-resolution 2D multichannel seismic (MCS) data at Green Canyon 955 (GC955) and Walker Ridge 313 (WR313). Based on previously collected logging-while-drilling (LWD) borehole data, these gas hydrate study sites are known to include high concentrations of gas hydrate within sand layers. At GC955 our new 2D data reveal at least three features that appear to be fluid-flow pathways (chimneys) responsible for gas migration and thus account for some aspects of the gas hydrate distribution observed in the LWD data. Our new data also show that the main gas hydrate target, a Pleistocene channel/levee complex, has an areal extent of approximately 5.5 square kilometers and that a volume of approximately 3 x 107 cubic meters of this body lies within the gas hydrate stability zone. Based on LWD-inferred values and reasonable assumptions for net sand, sand porosity, and gas hydrate saturation, we estimate a total equivalent gas-in-place volume of approximately 8 x 108 cubic meters for the inferred gas hydrate within the channel/levee deposits. At WR313 we are able to map the thin hydrate-bearing sand layers in considerably greater detail than that provided by previous data. We also can map the evolving and migrating channel feature that persists in this area. Together these data and the emerging results provide valuable new insights into the gas hydrate systems at these two sites.

  10. Gauge field theory approach to spin transport in a 2D electron gas

    B. Berche

    2009-01-01

    Full Text Available We discuss the Pauli Hamiltonian including the spin-orbit interaction within an U(1×SU(2 gauge theory interpretation, where the gauge symmetry appears to be broken. This interpretation offers new insight into the problem of spin currents in the condensed matter environment, and can be extended to Rashba and Dresselhaus spin-orbit interactions. We present a few outcomes of the present formulation: i it automatically leads to zero spin conductivity, in contrast to predictions of Gauge symmetric treatments, ii a topological quantization condition leading to voltage quantization follows, and iii spin interferometers can be conceived in which, starting from an arbitrary incoming unpolarized spinor, it is always possible to construct a perfect spin filtering condition.

  11. Quasi-One-Dimensional Electron Gas Bound to a Helium-Coated Nanotube

    Liebrecht, Michael; Del Maestro, Adrian; Cole, Milton W.

    2016-05-01

    A much-studied system is the quasi-2D electron gas in image-potential bound states at the surface of helium and hydrogen. In this paper, we report on an analogous quasi-1D system: electrons bound by image-like polarization forces to the surface of a helium-coated carbon nanotube. The potential is computed from an electron-helium pseudopotential, plus a dynamic image term evaluated from a semi-classical model of the nanotube's response function. Predictions are made for the bound states and potential many-body properties of this novel electron gas for a specific choice of tube radius and film thickness.

  12. Cold fusion in a dense electron gas

    Balian, R.; Blaizot, J.-R.; Bonche, P.

    1989-01-01

    We calculate the Coulomb penetration factor for two deuterons immersed in a dense electron gas. We find that electronic densities orders of magnitude larger than those which could be expected in metallic palladiun are required in order to bring the cold fusion rate to an observable value.

  13. Electronic structure of nanosized bcc Cu precipitates in Fe-Cu alloys studied by positron 2D-ACAR

    Based on the finding with the use of the coincidence Doppler measurements that the nanosized Cu precipitates are coherently embedded in the Fe-Cu matrix alloy, taking a bcc structure and acting as efficient positron traps, we measured 2D-ACARs of carefully grown and heat treated single crystals of Fe-Cu. We found that the precipitates have a Fermi surface with 12 necks touching the {110} Bragg planes of the bcc Brillouin zone, which contrasts distinctly with that of the bulk Cu with 8 necks touching the {111} Bragg planes of the fcc Brillouin zone. The 3 dimensional momentum reconstruction of the 2D-ACAR data showed that the Fermi surface cutoff of the Cu precipitates is blurred considerably as compared with that of bulk fcc Cu, suggesting a marked size effect in the momentum distribution. (orig.)

  14. Electron-beam-excited gas laser research

    Net energy gain in laser fusion places requirements on the laser that are not realized by any existing laser. Utilization of relativistic electron beams (REB's), a relatively new source for the excitation of gas laser media, may lead to new lasers that could satisfy these requirements. Already REB's have been utilized to excite gas laser media and produce gas lasers that have not been produced as successfully any other way. Electron-beam-excitation has produced electronic-transition dimer lasers that have not yet been produced by any other excitation scheme (for example, Xe2/ sup *(1)/, Kr:O(21S)/sup 2/, KrF/sup *(3)/). In addition, REB's have initiated chemical reactions to produce HF laser radiation with unique and promising results. Relativistic-electron-beam gas-laser research is continuing to lead to new lasers with unique properties. Results of work carried out at Sandia Laboratories in this pioneering effort of electron-beam-excited-gas lasers are reviewed. (U.S.)

  15. Design and implementation of gas puff imaging diagnostic to investigate 2D turbulence in the plasma of the COMPASS tokamak

    Cavalier, Jordan; Weinzettl, Vladimír; Varju, Jozef; Pánek, Radomír

    Prague: Czech Technical University in Prague, Faculty of Electrical Engineering, 2014. s. 21. [SPPT 2014 - 26th Symposium on Plasma Physics and Technology/26./. 16.06.2014-19.06.2014, Prague] Keywords : Tokamak edge plasma * gas-puff imaging * diagnostic Subject RIV: BL - Plasma and Gas Discharge Physics

  16. Electron energy deposition in carbon monoxide gas

    Liu, Weihong; Victor, G. A.

    1994-01-01

    A comprehensive set of electron impact cross sections for carbon monoxide molecules is presented on the basis of the most recent experimental measurements and theoretical calculations. The processes by which energetic electrons lose energy in CO gas are analyzed with these input cross sections. The efficiencies are computed of vibrational and electronic excitation, dissociation, ionization, and heating for CO gas with fractional ionization ranging from 0% to 10%. The calculated mean energy per ion pair for neutral CO gas is 32.3 eV, which is in excellent agreement with the experimental value of 32.2 eV. It increases to 35.6 eV at a fractional ionization of 1%, typical of supernovae ejecta.

  17. Magnetic properties of confined electron gas

    The effects of confinement by a two or three-dimensional harmonic potential on the magnetic properties of a free electron gas are investigated using the grand-canonical ensemble framework. At high temperatures an extension of Darwin's, Felderhof and Raval's works is made taking into account spin effects at low temperature. A comprehensive description of the magnetic properties of a free electron gas is given. The system is regarded as finite, but the boundary condition psi=0 is not introduced. The limits of weak and strong confinement are also analysed

  18. Seismic investigation of gas hydrates in the Gulf of Mexico: Results from 2013 high-resolution 2D and multicomponent seismic surveys

    Haines, S. S.; Hart, P. E.; Shedd, W. W.; Frye, M.; Agena, W.; Miller, J. J.; Ruppel, C. D.

    2013-12-01

    In the spring of 2013, the U.S. Geological Survey led a 16-day seismic acquisition cruise aboard the R/V Pelican in the Gulf of Mexico to survey two established gas hydrate study sites. We used a pair of 105/105 cubic inch generator/injector airguns as the seismic source, and a 450-m 72-channel hydrophone streamer to record two-dimensional (2D) data. In addition, we also deployed at both sites an array of 4-component ocean-bottom seismometers (OBS) to record P- and S-wave energy at the seafloor from the same seismic source positions as the streamer data. At lease block Green Canyon 955 (GC955), we acquired 400 km of 2-D streamer data, in a 50- to 250-m-spaced grid augmented by several 20-km transects that provide long offsets for the OBS. The seafloor recording at GC955 was accomplished by a 2D array of 21 OBS at approximately 400-m spacing, including instruments carefully positioned at two of the three boreholes where extensive logging-while-drilling data is available to characterize the presence of gas hydrate. At lease block Walker Ridge 313 (WR313), we acquired 450 km of streamer data in a set of 11-km, 150- to 1,000-m-spaced, dip lines and 6- to 8-km, 500- to 1000-m-spaced strike lines. These were augmented by a set of 20-km lines that provide long offsets for a predominantly linear array of 25 400- to 800-m spaced OBS deployed in the dip direction in and around WR313. The 2D data provide at least five times better resolution of the gas hydrate stability zone than the available petroleum industry seismic data from the area; this enables considerably improved analysis and interpretation of stratigraphic and structural features including previously unseen faults and gas chimneys that may have considerable impact on gas migration. Initial processing indicates that the OBS data quality is good, and we anticipate that these data will yield estimates of P- and S-wave velocities, as well as PP (reflected) and PS (converted wave) images beneath each sensor location.

  19. Seismic investigation of gas hydrates in the Gulf of Mexico: 2013 multi-component and high-resolution 2D acquisition at GC955 and WR313

    Haines, Seth S.; Hart, Patrick E.; Shedd, William W.; Frye, Matthew

    2014-01-01

    The U.S. Geological Survey led a seismic acquisition cruise at Green Canyon 955 (GC955) and Walker Ridge 313 (WR313) in the Gulf of Mexico from April 18 to May 3, 2013, acquiring multicomponent and high-resolution 2D seismic data. GC955 and WR313 are established, world-class study sites where high gas hydrate saturations exist within reservoir-grade sands in this long-established petroleum province. Logging-while-drilling (LWD) data acquired in 2009 by the Gulf of Mexico Gas Hydrates Joint Industry Project provide detailed characterization at the borehole locations, and industry seismic data provide regional- and local-scale structural and stratigraphic characterization. Significant remaining questions regarding lithology and hydrate saturation between and away from the boreholes spurred new geophysical data acquisition at these sites. The goals of our 2013 surveys were to (1) achieve improved imaging and characterization at these sites and (2) refine geophysical methods for gas hydrate characterization in other locations. In the area of GC955 we deployed 21 ocean-bottom seismometers (OBS) and acquired approximately 400 km of high-resolution 2D streamer seismic data in a grid with line spacing as small as 50 m and along radial lines that provide source offsets up to 10 km and diverse azimuths for the OBS. In the area of WR313 we deployed 25 OBS and acquired approximately 450 km of streamer seismic data in a grid pattern with line spacing as small as 250 m and along radial lines that provide source offsets up to 10 km for the OBS. These new data afford at least five times better resolution of the structural and stratigraphic features of interest at the sites and enable considerably improved characterization of lithology and the gas and gas hydrate systems. Our recent survey represents a unique application of dedicated geophysical data to the characterization of confirmed reservoir-grade gas hydrate accumulations.

  20. Gas supply system for the ''Electron'' installation

    The investigation results are described on a system for purifying and controlling the working gas of a helium streamer chamber operating on a bean of a electron linear accelerator. Maximum pressure in the system is 2 atm, and productivity at continuous helium circulation is 0.2 m2/hr. A chromatograph is used for determining the qualitative and quantitative composition of the gas. A gas-discharge cell is used for remote continuous control. Under operating conditions, the air impurity in the streamer chamber does not exceed 0.05%

  1. 2D x-ray imaging using a micro-pattern gas detector 'micro pixel chamber (μ-PIC)'

    The micro-pattern gas detector (MPGD) has a fine electrode structure, and it can obtain much higher positional resolution compared to that of the conventional gas detector based on the multi-wire proportional chamber. The 'Micro Pixel Chamber (μ-PIC)' is a new MPGD developed at Kyoto University. It has been applied not only to X-ray crystallographic analysis, but also particle and nuclear physics. In the present study, some experiments were conducted in order to evaluate the capability of μ-PIC in X-ray analysis. The gas gain of 3000 and linearity up to 200 kcps were obtained. Effect of parallax was examined, showing the image distortion within the theoretical estimate. Small angle X-ray scattering experiment using a collagen sample was also conducted, having demonstrated good X-ray imaging performance of μ-PIC. (author)

  2. Anomalous damping effects of magneto-quantum oscillations in the extremely 2D electronic system κ-(BEDT-TTF)2I3

    The electronic system of the organic superconductor κ-(BEDT-TTF)2I3 (BEDT-TTF=bis(ethylenedithiolo)tetrathi afulvalene) is identified as extremely two-dimensional (2D). The topology of the Fermi surface (FS) was investigated by means of Shubnikov-de Haas (SdH) as well as de Haas-van Alphen (dHvA) experiments focusing on the verification of the 2D character of the system. This two-dimensionality specially takes effect as soon as the magnetic field is oriented exactly perpendicular to the conducting planes (i.e. Θ=0 ). Under such conditions strong anomalous damping effects in the field and temperature dependence of quantum oscillation amplitudes are observed. These anomalous damping effects are discussed in terms of the occurrence of quasi-particle excitations with fractional statistics (QPFS) which may only occur in extremely 2D systems at high magnetic fields and low temperatures (i.e., only when ℎωC>>kBT). Taking up these requirements, the aim of this work is to quantify the extreme two-dimensionality of the electronic system of κ-(BEDT-TTF)2I3 and to show that the observed damping effects in fact are determined by the ratio ℎωC/kBT. These facts may support the interpretation of the observed damping effects of quantum oscillation amplitudes at high magnetic fields, low temperatures and Θ=0 as generated by the possible occurrence of such QPFS. (orig.)

  3. Primary uncleansed 2D versus primary electronically cleansed 3D in limited bowel preparation CT-colonography. Is there a difference for novices and experienced readers?

    The purpose of this study was to compare a primary uncleansed 2D and a primary electronically cleansed 3D reading strategy in CTC in limited prepped patients. Seventy-two patients received a low-fibre diet with oral iodine before CT-colonography. Six novices and two experienced observers reviewed both cleansed and uncleansed examinations in randomized order. Mean per-polyp sensitivity was compared between the methods by using generalized estimating equations. Mean per-patient sensitivity, and specificity were compared using the McNemar test. Results were stratified for experience (experienced observers versus novice observers). Mean per-polyp sensitivity for polyps 6 mm or larger was significantly higher for novices using cleansed 3D (65%; 95%CI 57-73%) compared with uncleansed 2D (51%; 95%CI 44-59%). For experienced observers there was no significant difference. Mean per-patient sensitivity for polyps 6 mm or larger was significantly higher for novices as well: respectively 75% (95%CI 70-80%) versus 64% (95%CI 59-70%). For experienced observers there was no statistically significant difference. Specificity for both novices and experienced observers was not significantly different. For novices primary electronically cleansed 3D is better for polyp detection than primary uncleansed 2D. (orig.)

  4. Magnetization Cooling of an Electron Gas

    Tsintsadze, Nodar L

    2012-01-01

    We propose an adiabatic magnetization process for cooling the Fermi electron gas to ultra-low temperatures as an alternative to the known adiabatic demagnetization mechanism. We show via a new adiabatic equation that at the constant density the increase of the magnetic field leads to the temperature decrease as $T\\sim 1/H^2$.

  5. Electron beam flue gas treatment process. Review

    The basis of the process for electron beam flue gas treatment are presented in the report. In tabular form the history of the research is reviewed. Main dependences of SO2 and NOx removal efficiencies on different physico-chemical parameters are discussed. Trends concerning industrial process implementation are presented in the paper,finally. (author). 74 refs, 11 figs, 1 tab

  6. Energy of the quasi-free electron in H{sub 2}, D{sub 2}, and O{sub 2}: Probing intermolecular potentials within the local Wigner-Seitz model

    Evans, C. M., E-mail: cherice.evans@qc.cuny.edu; Krynski, Kamil [Department of Chemistry and Biochemistry, Queens College – CUNY, Flushing, New York 11367 (United States); Streeter, Zachary; Findley, G. L., E-mail: findley@ulm.edu [School of Sciences, University of Louisiana at Monroe, Monroe, Louisiana 71209 (United States)

    2015-12-14

    We present for the first time the quasi-free electron energy V{sub 0}(ρ) for H{sub 2}, D{sub 2}, and O{sub 2} from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V{sub 0}(ρ) accurately in strongly absorbing fluids (e.g., O{sub 2}) and fluids with extremely low critical temperatures (e.g., H{sub 2} and D{sub 2}). We also show that the isotropic local Wigner-Seitz model for V{sub 0}(ρ) — when coupled with thermodynamic data for the fluid — can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths.

  7. Calculation of third-order signals via driven Schrödinger equations: General results and application to electronic 2D photon echo spectroscopy

    Highlights: ► Method for the calculation of optical signals via driven Schrodinger equations. ► The method accounts for arbitrary pulse durations and pulse-overlap effects. ► 2D spectra are calculated for systems with vibronic and electronic couplings - Abstract: We present the wavefunction (WF) version of the equation-of-motion phase-matching approach (EOM-PMA) for the calculation of four-wave-mixing (4WM) optical signals. For the material system, we consider a general electronic-vibrational Hamiltonian, comprising the electronic ground state, a manifold of singly-excited electronic states, and a manifold of doubly-excited electronic states. We show that the calculation of the third-order polarization for particular values of the pulse delay times and in a specific phase-matching direction requires 6 independent WF propagations within the rotating wave approximation. For material systems without optical transitions to doubly-excited electronic states, the number of WF propagations is reduced to 5. The WF EOM-PMA automatically accounts for pulse-overlap effects and allows the efficient numerical calculation of 4WM signals for vibronically coupled multimode material systems. The application of the method is illustrated for model systems with strong electron-vibrational and electronic inter-state couplings

  8. Origin of long-lived oscillations in 2D-spectra of a Quantum Vibronic Model: Electronic vs Vibrational coherence

    Plenio, M B; Huelga, S F

    2013-01-01

    We demonstrate that the coupling of excitonic and vibrational motion in biological complexes can provide mechanisms to explain the long-lived oscillations that have been obtained in non linear spectroscopic signals of different photosynthetic pigment protein complexes and we discuss the contributions of excitonic versus purely vibrational components to these oscillatory features. Considering a dimer model coupled to a structured spectral density we exemplify the fundamental aspects of the electron-phonon dynamics, and by analyzing separately the different contributions to the non linear signal, we show that for realistic parameter regimes purely electronic coherence is of the same order as purely vibrational coherence in the electronic ground state. Moreover, we demonstrate how the latter relies upon the excitonic interaction to manifest. These results link recently proposed microscopic, non-equilibrium mechanisms to support long lived coherence at ambient temperatures with actual experimental observations of...

  9. Time resolved, 2-D hard X-ray imaging of relativistic electron-beam target interactions on ETA-II

    Advanced radiographic applications require a constant source size less than 1 mm. To study the time history of a relativistic electron beam as it interacts with a bremsstrahlung converter, one of the diagnostics they use is a multi-frame time-resolved hard x-ray camera. They are performing experiments on the ETA-II accelerator at Lawrence Livermore National Laboratory to investigate details of the electron beam/converter interactions. The camera they are using contains 6 time-resolved images, each image is a 5 ns frame. By starting each successive frame 10 ns after the previous frame, they create a 6-frame movie from the hard x-rays produced from the interaction of the 50-ns electron beam pulse

  10. Spin Susceptibility of a 2D Electron System in GaAs towards the Weak Interaction Region

    Tan, Y. -W.; Zhu, J.; Stormer, H. L.; Pfeiffer, L. N.; Baldwin, K. W.; West, K.W.

    2005-01-01

    We determine the spin susceptibility $\\chi$ in the weak interaction regime of a tunable, high quality, two-dimensional electron system in a GaAs/AlGaAs heterostructure. The band structure effects, modifying mass and g-factor, are carefully taken into accounts since they become appreciable for the large electron densities of the weak interaction regime. When properly normalized, $\\chi$ decreases monotonically from 3 to 1.1 with increasing density over our experimental range from 0.1 to $4\\time...

  11. Exhaust gas treatment by electron beam irradiation

    Among global environmental problems, atmospheric pollution has been discussed since relatively old days, and various countermeasures have been taken, but recently in connection with acid rain, the efficient and economical treatment technology is demanded. As the denitration and desulfurization technology for the exhaust gas from the combustion of fossil fuel, the incineration of city trash and internal combustion engines, three is the treatment method by electron beam irradiation. By irradiating electron beam to exhaust gas, nitrogen oxides and sulfur oxides are oxidized to nitric acid and sulfuric acid, and by promoting the neutralization of these acids with injected alkali, harmless salts are recovered. This method has the merit that nitrogen oxides and surfur oxides can be removed efficiently with a single system. In this report, as for the exhaust gas treatment by electron beam irradiation, its principle, features, and the present status of research and development are described, and in particular, the research on the recent exhaust gas treatment in city trash incineration is introduced. This treatment method is a dry process, accordingly, waste water disposal is unnecessary. The reaction products are utilized as fertilizer, and waste is not produced. (K.I.)

  12. Two strongly correlated electron systems: the Kondo mode in the strong coupling limit and a 2-D model of electrons close to an electronic topological transition

    Two strongly correlated electron systems are considered in this work, Kondo insulators and high Tc cuprates. Experiments and theory suggest on one hand that the Kondo screening occurs on a rather short length scale and on the other hand that the Kondo coupling is renormalized to infinity in the low energy limit. The strong coupling limit is then the logical approach although the real coupling is moderate. A systematic development is performed around this limit in the first part. The band structure of these materials is reproduced within this scheme. Magnetic fluctuations are also studied. The antiferromagnetic transition is examined in the case where fermionic excitations are shifted to high energy. In the second part, the Popov and Fedotov representation of spins is used to formulate the Kondo and the antiferromagnetic Heisenberg model in terms of a non-polynomial action of boson fields. In the third part the properties of high Tc cuprates are explained by a change of topology of the Fermi surface. This phenomenon would happen near the point of optimal doping and zero temperature. It results in the appearance of a density wave phase in the under-doped regime. The possibility that this phase has a non-conventional symmetry is considered. The phase diagram that described the interaction and coexistence of density wave and superconductivity is established in the mean-field approximation. The similarities with the experimental observations are numerous in particular those concerning the pseudo-gap and the behavior of the resistivity near optimal doping. (author)

  13. Comparing the photophysics of the two forms of the Orange Carotenoid Protein using 2D electronic spectroscopy

    Mathies R.A.

    2013-03-01

    Full Text Available Broadband two-dimensional electronic spectroscopy is applied to investigate the photophysics of the photoactive orange carotenoid protein, which is involved in nonphotochemical quenching in cyanobacteria. Differences in dynamics between the light and dark forms arise from the different structure of the carotenoid in the protein pocket, with consequences for the biological role of the two forms.

  14. Orbital dependent Rashba splitting and electron-phonon coupling of 2D Bi phase on Cu(100) surface

    Gargiani, Pierluigi; Lisi, Simone; Betti, Maria Grazia [Dipartimento di Fisica, Università di Roma “La Sapienza,” Piazzale A. Moro 5, I-00185 Roma (Italy); Ibrahimi, Amina Taleb; Bertran, François; Le Fèvre, Patrick [Synchrotron SOLEIL, Saint-Aubin-BP 48, F-91192 Gif sur Yvette (France); Chiodo, Letizia [Center for Life Nano Science - Sapienza, Istituto Italiano di Tecnologia and European Theoretical Spectroscopy Facility (ETSF), Viale Regina Elena 291, I-00161, Roma (Italy)

    2013-11-14

    A monolayer of bismuth deposited on the Cu(100) surface forms a highly ordered c(2×2) reconstructed phase. The low energy single particle excitations of the c(2×2) Bi/Cu(100) present Bi-induced states with a parabolic dispersion in the energy region close to the Fermi level, as observed by angle-resolved photoemission spectroscopy. The electronic state dispersion, the charge density localization, and the spin-orbit coupling have been investigated combining photoemission spectroscopy and density functional theory, unraveling a two-dimensional Bi phase with charge density well localized at the interface. The Bi-induced states present a Rashba splitting, when the charge density is strongly localized in the Bi plane. Furthermore, the temperature dependence of the spectral density close to the Fermi level has been evaluated. Dispersive electronic states offer a large number of decay channels for transitions coupled to phonons and the strength of the electron-phonon coupling for the Bi/Cu(100) system is shown to be stronger than for Bi surfaces and to depend on the electronic state symmetry and localization.

  15. Engineering the electronic and magnetic properties of d(0) 2D dichalcogenide materials through vacancy doping and lattice strains.

    Ao, L; Pham, A; Xiao, H Y; Zu, X T; Li, S

    2016-03-01

    We have systematically investigated the effects of different vacancy defects in 2D d(0) materials SnS2 and ZrS2 using first principles calculations. The theoretical results show that the single cation vacancy and the vacancy complex like V-SnS6 can induce large magnetic moments (3-4 μB) in these single layer materials. Other defects, such as V-SnS3, V-S, V-ZrS3 and V-ZrS6, can result in n-type conductivity. In addition, the ab initio studies also reveal that the magnetic and conductive properties from the cation vacancy and the defect complex V-SnS6 can be modified using the compressive/tensile strain of the in-plane lattices. Specifically, the V-Zr doped ZrS2 monolayer can be tuned from a ferromagnetic semiconductor to a metallic/half-metallic material with decreasing/increasing magnetic moments depending on the external compressive/tensile strains. On the other hand, the semiconducting and magnetic properties of V-Sn doped SnS2 is preserved under different lattice compression and tension. For the defect complex like V-SnS6, only the lattice compression can tune the magnetic moments in SnS2. As a result, by manipulating the fabrication parameters, the magnetic and conductive properties of SnS2 and ZrS2 can be tuned without the need for chemical doping. PMID:26888010

  16. 2D numerical modelling of gas temperature in a nanosecond pulsed longitudinal He-SrBr2 discharge excited in a high temperature gas-discharge tube for the high-power strontium laser

    Chernogorova, T. P.; Temelkov, K. A.; Koleva, N. K.; Vuchkov, N. K.

    2016-05-01

    An active volume scaling in bore and length of a Sr atom laser excited in a nanosecond pulse longitudinal He-SrBr2 discharge is carried out. Considering axial symmetry and uniform power input, a 2D model (r, z) is developed by numerical methods for determination of gas temperature in a new large-volume high-temperature discharge tube with additional incompact ZrO2 insulation in the discharge free zone, in order to find out the optimal thermal mode for achievement of maximal output laser parameters. A 2D model (r, z) of gas temperature is developed by numerical methods for axial symmetry and uniform power input. The model determines gas temperature of nanosecond pulsed longitudinal discharge in helium with small additives of strontium and bromine.

  17. Electron-positron momentum density distribution of Gd from 2D ACAR data via maximum entropy and Cormack's methods

    Pylak, M. [Andrzej Soltan Institute for Nuclear Studies, Otwock-Swierk (Poland); Kontrym-Sznajd, G. [Polish Academy of Sciences, Institute of Low Temperature and Structure Research, P.O. Box 937, Wroclaw 2 (Poland); Dobrzynski, L. [Andrzej Soltan Institute for Nuclear Studies, Otwock-Swierk (Poland); University of Bialystok, Faculty of Physics, Bialystok (Poland)

    2011-08-15

    A successful application of the maximum entropy method (MEM) to the reconstruction of electron-positron momentum density distribution in gadolinium out of the experimental of 2D ACAR data is presented. Formally, the algorithm used was prepared for two-dimensional reconstructions from line integrals. For the first time the results of MEM, applied to such data, are compared in detail with the ones obtained by means of Cormack's method. It is also shown how the experimental uncertainties may influence the results of the latter analysis. Preliminary calculations, using WIEN2k code, of band structure and Fermi surface have been done as well. (orig.)

  18. The effective mass and g-factor of the strongly correlated 2-D electron fluid. Evidence for a coupled-valley condensate in the Si system

    Dharma-wardana, M. W. C.

    2003-01-01

    The effective mass m*, and the Lande g-factor of the uniform 2-D electron fluid (2DEF) are calculated as a function of the spin polarization zeta, and the density parameter r_s, using a non-perturbative analytic approach. Our theory is in good accord with the m*g* data of Zhu et al. for zeta=0 for the GaAs-2DEF, and striking agreement with the data of Shashkin et al for the Si-2DEF. While g* is enhanced in GaAs, m* is enhanced in Si. The latter arises from singlet-pair excitations in the two ...

  19. Quantitative electron and gas cloud experiments

    Electrons can accumulate in and degrade the quality of positively charged beams. This is a well-known problem in proton storage rings. Heavy-ion rings are more frequently limited by gas pressure-rise effects. Both effects may limit how closely the beam radius can approach the beam-tube radius in a heavy-ion linac. We study beams of 1 MeV K+ with currents of up to 180 mA in the High-Current Experiment (HCX), and compare our work with simulations. The theory and simulation results are discussed in a companion papers. We have developed the first diagnostics that quantitatively measure the accumulation of electrons in a beam [M. Kireeff Covo, A. Molvik, A. Friedman, J.-L. Vay, P. Seidl, G. Logan, D. Baca, J.L. Vujic, Phys. Rev. Lett. 97 (2006) 054801; M. Kireeff Covo, et al., Nucl. Instr. and Meth. A, 2007, in press, doi:10.1016/j.nima.2007.02.045.]. This will enable the particle balance to be measured for each source of electrons in a linac: ionization of gas, emission from walls surrounding the beam, and emission from an end wall coupled with electron drifts upstream through quadrupole magnets, and electron-trapping efficiencies can be determined. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We discuss plans for experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap electrons within the magnets. We observe oscillations of the electron density and position in the last quadrupole magnet when we flood the beam with electrons from an end wall. These oscillations, near 6 MHz, are observed to grow from the center of the magnet while drifting upstream against the beam, in good agreement with simulations

  20. Electronic Desorption of gas from metals

    Molvik, A W; Kollmus, H; Mahner, E; Covo, M K; Bender, M; Bieniosek, F M; Kramer, A; Kwan, J; Prost, L; Seidl, P A; Westenskow, G

    2006-11-02

    During heavy ion operation in several particle accelerators world-wide, dynamic pressure rises of orders of magnitude were triggered by lost beam ions that bombarded the vacuum chamber walls. This ion-induced molecular desorption, observed at CERN, GSI, and BNL, can seriously limit the ion beam lifetime and intensity of the accelerator. From dedicated test stand experiments we have discovered that heavy-ion induced gas desorption scales with the electronic energy loss (dE{sub e}/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering.

  1. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  2. Circular polarisation measurements of the L sub. alpha. cascade radiation for the 3 sup 2 D sub j states of atomic hydrogen, excited by electron impact

    Farrell, D.; Slevin, J. (Saint Patrick' s Coll., Maynooth (Ireland)); Chwirot, S. (Uniwersytet Mikolaja Kopernika, Torun (Poland). Inst. Fizyki); Srivastava, R. (Roorkee Univ. (India). Dept. of Physics)

    1990-01-28

    Measurements are reported for the circular polarisation of the L{sub {alpha}} radiation arising from the cascade of the 3{sup 2}D{sub j} states of atomic hydrogen to the 2{sup 2}P{sub j} states detected in coincidence with electrons with n = 3 energy loss. Data for the atomic orientation parameter L {sub perpendicular} are presented at incident electron energies of 54.4 and 100 eV and at scattering angles {theta}{sub e} of 20{sup 0} and 25{sup 0}. These data, together with previous measurements for this transition, constitute a determination of the complete parameter set {l brace}{gamma}, P{sub 1}, {rho}{sub 00}, L {sub perpendicular}{r brace} for 3{sup 2}D{sub j} excitations in this dynamic range. Calculations for P{sub 3} and L {sub perpendicular} using distorted-wave approximation theory are also performed. The theoretical results are presented and compared with the experimental data. (author).

  3. Characterization of Muscat wines aroma evolution using comprehensive gas chromatography followed by a post-analytic approach to 2D contour plots comparison.

    Bordiga, Matteo; Rinaldi, Maurizio; Locatelli, Monica; Piana, Gianluca; Travaglia, Fabiano; Coïsson, Jean Daniel; Arlorio, Marco

    2013-09-01

    This study presents the application of a headspace solid-phase microextraction (HS-SPME) method on the analysis of Muscat-based wines volatiles by comprehensive two-dimensional gas chromatography (GC×GC) and Time-Of-Flight mass spectrometry (TOF-MS). The aroma patterns were established for different samples of Asti Spumante and Moscato d'Asti wines, stored in bottles for 6 months at different temperatures. Wines stored at 5 °C for 6 months did not show significant changes in flavor; otherwise, the samples stored at 15 and 25 °C, showed a significant decrease in linalool, β-damascenone, ethyl hexanoate, and ethyl octanoate levels. In these last samples, α-terpineol, hotrienol, nerol oxide, furanic linalool oxides A/B and rose oxide concentrations significantly increased. A mathematical approach was developed and applied to raw data exported after the chromatographic course, in order (i) to normalise different 2D chromatograms, permitting their direct comparison and (ii) to automatically identify and calculate from pixel-to-pixel re-designed 2D chromatograms any differences among key volatile compounds. PMID:23578615

  4. Evaluation of gas radiation heat transfer in a 2D axisymmetric geometry using the line-by-line integration and WSGG models

    The weighted-sum-of-gray-gases (WSGG) model is widely used in engineering computations of radiative heat transfer due to its relative simplicity, robustness and flexibility. This paper presents the computation of radiative heat transfer in a 2D axisymmetric chamber using two WSGG models to compute radiation in H2O and CO2 mixtures. The first model considers a fixed ratio between the molar concentrations of H2O and CO2, while the second allows the solution for arbitrary ratios. The correlations for both models are based on the HITEMP2010 database. The test case considers typical conditions found in turbulent methane flames, with steep variations in the temperature field as well as in the molar concentrations of the participating species. To assess the accuracy of the WSGG model, the results are compared with a solution obtained by line-by-line integration (LBL) of the spectrum. - Highlights: • The paper presents solutions of radiative heat transfer in a 2D axisymmetric chamber. • The temperature and concentration fields are representative of methane turbulent flames. • Solutions from line-by-line integration of the RTE are presented for evaluation of gas models. • WSGG models considering constant and non-constant pressure ratios of H2O and CO2 are employed. • Solutions from the WSGG models proved to be accurate for the proposed test case

  5. A 2D multiwavelength study of the ionized gas and stellar population in the giant H II region NGC 588

    Monreal-Ibero, A.; Relaño, M.; Kehrig, C.; Pérez-Montero, E.; Vílchez, J. M.; Kelz, A.; Roth, M. M.; Streicher, O.

    2011-05-01

    Giant H II regions (GHIIRs) in nearby galaxies are a local sample in which we can study in detail processes in the interaction of gas, dust and newly formed stars which are analogous to those which occurred in episodes of higher intensity in which much of the current stellar population was born. Here, we present an analysis of NGC 588, a GHIIR in M33, based on optical Integral Field Spectroscopy data obtained with the Potsdam Multi-Aperture Spectrophotometer at the 3.5-m telescope of the Calar Alto Observatory, CAHA, together with Spitzer infrared images at 8 and 24 μm. The extinction distribution measured in the optical shows complex structure, with three maxima which correlate in position with those of the emission at 24 and 8 μm. Furthermore, the Hα luminosity absorbed by the dust within the H II region reproduces the structure observed in the 24-μm image, supporting the use of the 24-μm band as a valid tracer of recent star formation. A velocity difference of ˜50 km s-1 was measured between the areas of high and low surface brightness, which would be expected if NGC 588 were an evolved GHIIR. We have carefully identified the areas which contribute most to the line ratios measured in the integrated spectrum. Those line ratios which are used in diagnostic diagrams proposed by Baldwin, Phillips & Terlevich (i.e. the BPT diagrams) show a larger range of variation in the low surface brightness areas. The ranges are ˜0.5-1.2 dex for [N II]λ6584/Hα, 0.7-1.7 dex for [S II]λλ6717,6731/Hα and 0.3-0.5 dex for [O III]λ5007/Hβ, with higher values of [N II]λ6584/Hα and [S II]λλ6717,6731/Hα, and lower values of [O III]λ5007/Hβ in the areas of lower surface brightness. Ratios corresponding to large ionization parameter (U) are found between the peak of the emission in Hβ and the main ionizing source decreasing radially outwards within the region. Differences between the integrated and local values of the U tracers can be as high as ˜0.8 dex, notably when

  6. Relativistic Thermodynamics of Magnetized Fermi Electron Gas

    Tsintsadze, Nodar L

    2012-01-01

    To study the relativistic thermodynamic properties of a Fermi gas in a strong magnetic field, we construct the relativistic thermodynamic potential by the relativistic Fermi distribution function taking into account that the motion of particles in a plane perpendicular to the magnetic field is quantized. With this general potential at hand, we investigate all the thermodynamic quantities as a function of densities, temperatures and the magnetic field. We obtain a novel set of adiabatic equations. Having the expression of the pressure and adiabatic state equations, we determine the sound velocity for several cases revealing a new type of sound velocity. Finally, we disclose the magnetic cooling in the quantized electron Fermi gas, which is based on an adiabatic magnetization in contrast to the known adiabatic demagnetization.

  7. Progress with the gas electron multiplier

    Offering position accuracies of few tens of microns and rate capabilities close to a MHz mm-2, detectors using the Gas Electron Multiplier (GEM) as amplifying element are attractive whenever a precise knowledge of the energy loss topology is required. Moreover, they are robust and easy to manufacture. Cascading two or more GEM foils permits to achieve larger gains and reliable operation in harsh operating conditions. We discuss the operating principles and the major performances of the new devices, particularly in view of their possible use for particle identification in Transition Radiation and Cherenkov ring imaging detectors

  8. Off-axis electron holography with a dual-lens imaging system and its usefulness in 2-D potential mapping of semiconductor devices

    A variable magnification electron holography, applicable for two-dimensional (2-D) potential mapping of semiconductor devices, employing a dual-lens imaging system is described. Imaging operation consists of a virtual image formed by the objective lens (OL) and a real image formed in a fixed imaging plane by the objective minilens. Wide variations in field of view (100-900 nm) and fringe spacing (0.7-6 nm) were obtained using a fixed biprism voltage by varying the total magnification of the dual OL system. The dual-lens system allows fringe width and spacing relative to the object to be varied roughly independently from the fringe contrast, resulting in enhanced resolution and sensitivity. The achievable fringe width and spacing cover the targets needed for devices in the semiconductor technology road map from the 350 to 45 nm node. Two-D potential maps for CMOS devices with 220 and 70 nm gate lengths were obtained

  9. Off-axis electron holography with a dual-lens imaging system and its usefulness in 2-D potential mapping of semiconductor devices.

    Wang, Y Y; Kawasaki, M; Bruley, J; Gribelyuk, M; Domenicucci, A; Gaudiello, J

    2004-11-01

    A variable magnification electron holography, applicable for two-dimensional (2-D) potential mapping of semiconductor devices, employing a dual-lens imaging system is described. Imaging operation consists of a virtual image formed by the objective lens (OL) and a real image formed in a fixed imaging plane by the objective minilens. Wide variations in field of view (100-900 nm) and fringe spacing (0.7-6 nm) were obtained using a fixed biprism voltage by varying the total magnification of the dual OL system. The dual-lens system allows fringe width and spacing relative to the object to be varied roughly independently from the fringe contrast, resulting in enhanced resolution and sensitivity. The achievable fringe width and spacing cover the targets needed for devices in the semiconductor technology road map from the 350 to 45 nm node. Two-D potential maps for CMOS devices with 220 and 70 nm gate lengths were obtained. PMID:15450653

  10. Influence of the screening effect onto the transport parameters of hot 2D electrons in n-GaAs square quantum wells

    Zandler, G.; Vass, E.

    1989-10-01

    The heating temperature ΔTe , the drift velocity vd , the average momentum-loss rate , and the average energy-loss rate of hot 2-D electrons interacting simultaneously with polar optical phonons and ionized impurities are calculated as a function of the lattice temperature T, the carrier concentration n, and the external electric field E. The calculations are carried out with unscreened and screened interaction matrix elements including plasmon-phonon coupling. A hot drifted Fermi-Dirac distribution is used to evaluate and , as well as the dielectric screening function in the random-phase approximation. The distribution-function parameters vd and Te are determined self-consistently by solving simultaneously the power- and force-balance equations.

  11. Electronic band structure and charge density wave transition in quasi-2D KMo{sub 6}O{sub 17} purple bronze

    Valbuena, M A [Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid (Spain); Avila, J; Asensio, M C [Synchrotron SOLEIL, L' Orme des Merisiers, Saint-Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex (France); Vyalikh, D V; Laubschat, C; Molodtsov, S L [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany); Guyot, H [LEPES, CNRS, BP 166, 38042 Grenoble Cedex 9 (France)], E-mail: mvbuena@icmm.csic.es

    2008-03-15

    High resolution angle-resolved photoemission of quasi-2D KMo{sub 6}O{sub 17} purple bronze has been performed in the range from room temperature to 130 K, slightly above the charge density wave (CDW) transition (T{sub c} = 110 K), and down to 35 K (well below T{sub c}). In this paper we report a detailed study of how electronic band structure is affected by this transition driven by the hidden nesting scenario. The expected spectroscopic fingerprints of the CDW phase transition have been found and discussed according to the hidden one dimension and the development of a quasi-commensurate CDW. The excellent agreement between theory and our experimental results makes of potassium purple bronze a reference system for studying this type of instabilities.

  12. Electronic Structure and Fermi Surface of the Quaternary Intermetallic Borocarbide Superconductor YNi2B2C from 2D-ACAR

    Hamid, A. S.

    We measured the angular momentum density distribution of YNi2B2C to acquire information about its electronic structure. The measurements were performed using the full-scale utility of the two-dimensional angular correlation of annihilation radiation (2D-ACAR). The measured spectra clarified that Ni (3d) like state, predominantly, affected the Fermi surface of YNi2B2C. Further, s- and p-like-states enhanced its superconducting properties. The Fermi surface of YNi2B2C. was reconstructed using Fourier transformation followed by the LCW (Loucks, Crisp and West) folding procedure. It showed a large and complex surface similar to that of the high temperature superconductors HTS, with anisotropic properties. It also disclosed the effect of d-like state. Nevertheless, the current Fermi surface could deliver the needed topological information to isolate its features. The general layouts of this Fermi surface are; two large electron surfaces running along Γ-Z direction; as well as an additional large electron surface centered on X point; beside one hole surface centered on 100 point. This Fermi surface was interpreted in view of the earlier results.

  13. Influence of electron-neutral elastic collisions on the instability of an ion-contaminated cylindrical electron cloud: 2D3V PIC-with-MCC simulations

    Sengupta, Meghraj

    2016-01-01

    This paper is a simulation based investigation of the effect of elastic collisions and effectively elastic-like excitation collisions between electrons and background neutrals on the dynamics of a cylindrically trapped electron cloud that also has an ion contaminant mixed in it. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the ion resonance instability caused by the presence of background neutrals as compared to a vacuum background. Further in order to understand if the non-ionizing collisions can independently be a cause of destabilization of an electron cloud, a second set of numerical experiments were performed with pure electron plasmas making non-ionizing collisions with different densities of background neutrals. These experiments reveal that the nature of potential energy extraction from the electron cloud by the non-ionizing collisions is not similar to the potential energy extraction of other destabilizing processes \\textit{e.g.} a resi...

  14. The Making of RSG-GAS Technical Document Electronic Files

    The RSG-GAS technical document electronic files are needed to support ageing assessment on RSG-GAS systems and components. Making of the electronic files are using Deskan scanner. The technical documents are resulted from scanned tracing paper drawings from size A4 to A0 in the document room. The technical documents result are electronic drawing files of RSG-GAS reactor pool components with file extension *.pcx. With electronic files, finding and reproducing the RSG-GAS technical documents will be easier to be done and it is can support ageing assessment on RSG-GAS components. (author)

  15. Effects of the electron-electron interaction in the spin resonance in 2D systems with Dresselhaus spin-orbit coupling

    Krishtopenko, S. S., E-mail: sergey.krishtopenko@mail.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-02-15

    The effect of the electron-electron interaction on the spin-resonance frequency in two-dimensional electron systems with Dresselhaus spin-orbit coupling is investigated. The oscillatory dependence of many-body corrections on the magnetic field is demonstrated. It is shown that the consideration of many-body interaction leads to a decrease or an increase in the spin-resonance frequency, depending on the sign of the g factor. It is found that the term cubic in quasimomentum in Dresselhaus spin-orbit coupling partially decreases exchange corrections to the spin resonance energy in a two-dimensional system.

  16. Electron beam application in gas waste treatment in China

    In the most recent decade, electron beam waste treatment technology attracted serious attention from environment policymaker and industrial leaders in power industry in China. Starting in middle of 1980's, Chinese research institute began experiment of electron beam treatment on flue gas. By the end of 2000, two 10,000 cubic meters per hour small scale electron beam gas purifying station were established in Sichuang province and Beijing. Several electron beam gas purifying demonstration projects are under construction. With robust economy and strong energy demand, needless to say, in near future, electron beam gas purifying technology will have a bright prospect in China. (author)

  17. Influence of electron-neutral elastic collisions on the instability of an ion-contaminated cylindrical electron cloud: 2D3V PIC-with-MCC simulations

    Sengupta, Meghraj; Ganesh, Rajaraman

    2016-01-01

    This paper is a simulation based investigation of the effect of elastic collisions and effectively elastic-like excitation collisions between electrons and background neutrals on the dynamics of a cylindrically trapped electron cloud that also has an ion contaminant mixed in it. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the ion resonance instability caused by the presence of background neutrals as compared to a vacuum backgro...

  18. Gas and dust in the star-forming region rho Oph A: The dust opacity exponent beta and the gas-to-dust mass ratio g2d

    Liseau, R; Lunttila, T; Olberg, M; Rydbeck, G; Bergman, P; Justtanont, K; Olofsson, G; de Vries, B L

    2015-01-01

    We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent beta for spatial and/or temporal variations. Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution ...

  19. Electron acceleration by laser fields in a gas

    This report discusses: electron acceleration by passes through a Gaussian-mode laser beam in an index matching gas; electron beam dynamics in gas media; energy loss and scattered trajectory simulations for electrons in gases; interaction within an optical waveguide; refractive index enhancement techniques; and collaboration with STI Optronics

  20. Heat diffusion in the disordered electron gas

    Schwiete, G.; Finkel'stein, A. M.

    2016-03-01

    We study the thermal conductivity of the disordered two-dimensional electron gas. To this end, we analyze the heat density-heat density correlation function concentrating on the scattering processes induced by the Coulomb interaction in the subtemperature energy range. These scattering processes are at the origin of logarithmic corrections violating the Wiedemann-Franz law. Special care is devoted to the definition of the heat density in the presence of the long-range Coulomb interaction. To clarify the structure of the correlation function, we present details of a perturbative calculation. While the conservation of energy strongly constrains the general form of the heat density-heat density correlation function, the balance of various terms turns out to be rather different from that for the correlation functions of other conserved quantities such as the density-density or spin density-spin density correlation function.

  1. Gas and dust in the star-forming region ρ Oph A. The dust opacity exponent β and the gas-to-dust mass ratio g2d

    Liseau, R.; Larsson, B.; Lunttila, T.; Olberg, M.; Rydbeck, G.; Bergman, P.; Justtanont, K.; Olofsson, G.; de Vries, B. L.

    2015-06-01

    Aims: We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods: Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+ (J = 3-2) and (J = 6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. Results: The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, = 88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions: Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C18O, also N2H+ is frozen onto the grains. Based on observations with APEX, which is a 12 m diameter submillimetre telescope at 5100 m altitude on Llano Chajnantor

  2. The warm ionized gas in CALIFA early-type galaxies: 2D emission-line patterns and kinematics for 32 galaxies

    Gomes, J M; Kehrig, C; Vílchez, J M; Lehnert, M D; Sánchez, S F; Ziegler, B; Breda, I; Reis, S N dos; Iglesias-Páramo, J; Bland-Hawthorn, J; Galbany, L; Bomans, D J; Rosales-Ortega, F F; Fernandes, R Cid; Walcher, C J; Falcón-Barroso, J; García-Benito, R; Márquez, I; del Olmo, A; Masegosa, J; Mollá, M; Marino, R A; Delgado, R M González; López-Sánchez, Á R

    2015-01-01

    The morphological, spectroscopic and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive, quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer an unprecedented opportunity for advancing our understanding of the wim in ETGs. This article centers on a 2D investigation of the wim component in 32 nearby (<~150Mpc) ETGs from CALIFA, complementing a previous 1D analysis of the same sample (Papaderos et al. 2013; P13). We include here H\\alpha\\ intensity and equivalent width (EW) maps and radial profiles, diagnostic emission-line ratios, besides ionized-gas and stellar kinematics. This study is supplemented by \\tau-ratio maps as an efficient means to quantify the role of photoionization by pAGB stars, as compared to other mechanisms (e.g., AGN, low-level star formation). Additio...

  3. Electron-Phonon Scattering in Semiconductor Structures with One-Dimensional Electron Gas

    Pozdnyakov, Dmitry; Galenchik, Vadim

    2006-01-01

    In this study a method for calculation of the electron-phonon scattering rate in semiconductor structures with one-dimensional electron gas is developed. The energy uncertainty of electrons is taken into account.

  4. Tailoring the nature and strength of electron-phonon interactions in the SrTiO3(001) 2D electron liquid

    Wang, Z.; McKeown Walker, S.; Tamai, A.; Wang, Y.; Ristic, Z.; Bruno, F. Y.; de la Torre, A.; Riccò, S.; Plumb, N. C.; Shi, M.; Hlawenka, P.; Sánchez-Barriga, J.; Varykhalov, A.; Kim, T. K.; Hoesch, M.; King, P. D. C.; Meevasana, W.; Diebold, U.; Mesot, J.; Moritz, B.; Devereaux, T. P.; Radovic, M.; Baumberger, F.

    2016-08-01

    Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron-phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

  5. An evolution from 3D face-centered-cubic ZnSnO3 nanocubes to 2D orthorhombic ZnSnO3 nanosheets with excellent gas sensing performance

    We have successfully observed the development of three-dimensional (3D) face-centered-cubic ZnSnO3 into two-dimensional (2D) orthorhombic ZnSnO3 nanosheets, which is the first observation of 2D ZnSnO3 nanostructures to date. The synthesis from 3D to 2D nanostructures is realized by the dual-hydrolysis-assisted liquid precipitation reaction and subsequent hydrothermal treatment. The time-dependent morphology indicates the transformation via a ‘dissolution–recrystallization’ mechanism, accompanied by a ‘further growth’ process. Furthermore, the 2D ZnSnO3 nanosheets consist of smaller sized nanoflakes. This further increases the special specific surface area and facilitates their application in gas sensing. The 2D ZnSnO3 nanosheets exhibit excellent gas sensing properties, especially through their ultra-fast response and recovery. When exposed to ethanol and acetone, the response rate is as fast as 0.26 s and 0.18 s, respectively, and the concentration limit can reach as low as 50 ppb of ethanol. All these results are much better than those reported so far. Our experimental results indicate an efficient approach to realize high-performance gas sensors. (paper)

  6. CHEM2D-OPP: A new linearized gas-phase ozone photochemistry parameterization for high-altitude NWP and climate models

    J. P. McCormack

    2006-01-01

    Full Text Available The new CHEM2D-Ozone Photochemistry Parameterization (CHEM2D-OPP for high-altitude numerical weather prediction (NWP systems and climate models specifies the net ozone photochemical tendency and its sensitivity to changes in ozone mixing ratio, temperature and overhead ozone column based on calculations from the CHEM2D interactive middle atmospheric photochemical transport model. We evaluate CHEM2D-OPP performance using both short-term (6-day and long-term (1-year stratospheric ozone simulations with the prototype high-altitude NOGAPS-ALPHA forecast model. An inter-comparison of NOGAPS-ALPHA 6-day ozone hindcasts for 7 February 2005 with ozone photochemistry parameterizations currently used in operational NWP systems shows that CHEM2D-OPP yields the best overall agreement with both individual Aura Microwave Limb Sounder ozone profile measurements and independent hemispheric (10°–90° N ozone analysis fields. A 1-year free-running NOGAPS-ALPHA simulation using CHEM2D-OPP produces a realistic seasonal cycle in zonal mean ozone throughout the stratosphere. We find that the combination of a model cold temperature bias at high latitudes in winter and a warm bias in the CHEM2D-OPP temperature climatology can degrade the performance of the linearized ozone photochemistry parameterization over seasonal time scales despite the fact that the parameterized temperature dependence is weak in these regions.

  7. Optoelectronics with 2D semiconductors

    Mueller, Thomas

    2015-03-01

    Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies.

  8. Spin polarization of two-dimensional electronic gas decoupled from structural asymmetry environment

    Pieczyrak, B.; Szary, M.; Jurczyszyn, L.; Radny, M. W.

    2016-05-01

    It is shown, using density functional theory, that a 2D electron gas induced in a monolayer of Pb or Tl adatoms on the Si (111 )-1 ×1 surface is insensitive to the structural asymmetry of the system and its spin polarization is governed by the interaction between the adlayer and the substrate. It is demonstrated that this interaction changes the in-plane inversion symmetry of the charge distribution within the monolayer and can either suppress [Pb/Si(111)] or enhance [Tl/Si(111)] the adatom intra-atomic spin-orbit effect on a Rashba-Bychkov-type spin splitting.

  9. Effects of electron beam irradiation on tin dioxide gas sensors

    Zheng Jiao; Xiaojuan Wan; Bing Zhao; Huijiao Guo; Tiebing Liu; Minghong Wu

    2008-02-01

    In this paper, the effects of electron beam irradiation on the gas sensing performance of tin dioxide thin films toward H2 are studied. The tin dioxide thin films were prepared by ultrasonic spray pyrolysis. The results show that the sensitivity increased after electron beam irradiation. The electron beam irradiation effects on tin dioxide thin films were simulated and the mechanism was discussed.

  10. Analysis of tubes filled with charged electron gas

    Karrmann, Stefan

    2011-01-01

    We show that tubes filled with electron gas, as presented by A.Bolonkin, are not possible with current materials. First, the pressure of the charges on the outer surface cancel almost all of the electrostatic pressure of the inner electrons. Second, due to the mutually repulsion most of the electrons are in the outmost shell of the tube and not individually free.

  11. Perspectives for spintronics in 2D materials

    Wei Han

    2016-03-01

    Full Text Available The past decade has been especially creative for spintronics since the (rediscovery of various two dimensional (2D materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.

  12. Perspectives for spintronics in 2D materials

    Han, Wei

    2016-03-01

    The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.

  13. Effect of Laughlin correlations on crystalline mean field solutions for the 2D electron gas in a strong magnetic field

    The energy per particle of a many body wavefunction that mixes Laughlin liquid with crystalline correlations is estimated in the thermodynamic limit. The Monte Carlo algorithm is employed. The wave function is constructed in such a way that it has the same zeroes as the Laughlin state. Results with up to 16 particles show that our trial wavefunction has lower energy than Laughlin's. Preliminary results for 36 particles suggest that this tendency could reach the thermodynamic limit. (author)

  14. Electrothermal gas generator: Development and qualification of the control electronics

    Matthaeus, G.; Schmitz, H. D.

    1986-07-01

    The development and qualification of an electronic control circuitry for an electrothermal or catalytic hydrazine gas generator system is described. The circuitry, named manual override, controls the gas pressure in a tank using a pressure transducer and the gas generator to keep the pressure constant within narrow tolerances. The present pressure can be varied by ground command, enabling a variable thrust of the gas fed cold gas thrusters. The automatic loop can be switched off and the tank pressure be controlled by ground command. Two manual overrides SN01 and SN02 were qualified.

  15. Electron-beam pumping of visible and ultraviolet gas lasers

    Several techniques for using direct electron-pumping of gas lasers are reviewed. The primary objective is to categorize pump geometries and to give guidelines for gun selection and pulser design. Examples and application of pump technology are given

  16. Ferromagnetism in an Electron Gas Obeying Fractional Statistics

    杨凯华; 韩汝珊; 王玉鹏

    2001-01-01

    We study an ideal electron gas obeying fractional statistics. The parameters for exclusion statistics are given by the strength of the repulsive interactions. In some parameter regions, it is found the system shows itinerant ferromagnetism.

  17. Electronic data interchange in the Canadian natural gas industry

    The concept of electronic data interchange (EDI) in the gas industry was discussed. EDI as a champion of costumer service and as a powerful management tool was defined, and the process of electronic information transfer was explained. EDI was then placed in the context of the business process, and its benefits in providing efficient service and product improvement were enumerated. North American Gas EDI standards, and industry initiatives were explored in detail

  18. Electromagnetic drift modes in an inhomogeneous electron gas

    Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens

    1986-01-01

    A pair of nonlinear equations is derived which describes the dynamics of the electromagnetic drift oscillations in a nonuniform magnetized electron gas. It is shown that the nonlinear electromagnetic drift modes can propagate in the form of dipole vortices......A pair of nonlinear equations is derived which describes the dynamics of the electromagnetic drift oscillations in a nonuniform magnetized electron gas. It is shown that the nonlinear electromagnetic drift modes can propagate in the form of dipole vortices...

  19. Electrothermal energy conversion using electron gas volumetric change inside semiconductors

    Yazawa, K.; Shakouri, A.

    2016-07-01

    We propose and analyze an electrothermal energy converter using volumetric changes in non-equilibrium electron gas inside semiconductors. The geometric concentration of electron gas under an electric field increases the effective pressure of the electrons, and then a barrier filters out cold electrons, acting like a valve. Nano- and micro-scale features enable hot electrons to arrive at the contact in a short enough time to avoid thermalization with the lattice. Key length and time scales, preliminary device geometry, and anticipated efficiency are estimated for electronic analogs of Otto and Brayton power generators and Joule-Thomson micro refrigerators on a chip. The power generators convert the energy of incident photons from the heat source to electrical current, and the refrigerator can reduce the temperature of electrons in a semiconductor device. The analytic calculations show that a large energy conversion efficiency or coefficient of performance may be possible.

  20. 2D numerical modelling of the gas temperature in a high-temperature high-power strontium atom laser excited by nanosecond pulsed longitudinal discharge in a He-SrBr2 mixture

    Chernogorova, T. P.; Temelkov, K. A.; Koleva, N. K.; Vuchkov, N. K.

    2014-05-01

    Assuming axial symmetry and a uniform power input, a 2D model (r, z) is developed numerically for determination of the gas temperature in the case of a nanosecond pulsed longitudinal discharge in He-SrBr2 formed in a newly-designed large-volume high-temperature discharge tube with additional incompact ZrO2 insulation in the discharge-free zone, in order to find the optimal thermal mode for achievement of maximal output laser parameters. The model determines the gas temperature of a nanosecond pulsed longitudinal discharge in helium with small additives of strontium and bromine.

  1. Images of triple gas electron multiplier with pixel-pads

    Testing of a triple gas electron multiplier (GEM) with pixel-pads is described. Images by scanning and suspending radioactive sources were obtained by using 96 channels digital data acquisition (DAQ) system which was composed of 96 8 × 8 mm2 pads and associated electronics channels. (nuclear physics)

  2. High power electron accelerators for flue gas treatment

    Flue gas treatment process based on electron beam application for SO2 and NOx removal was successfully demonstrated in number of laboratories, pilot plants and industrial demonstration facilities. The industrial scale application of an electron beam process for flue gas treatment requires accelerators modules with a beam power 100-500 kW and electron energy range 0.8-1.5 MeV. The most important accelerator parameters for successful flue gas radiation technology implementation are related to accelerator reliability/availability, electrical efficiency and accelerator price. Experience gained in high power accelerators exploitation in flue gas treatment industrial demonstration facility was described and high power accelerator constructions have been reviewed. (author)

  3. Dosimetry for combustion flue gas treatment with electron beam

    The electron beam treatment of flue gas is one of the new technologies. There are several reasons for carrying out dosimetry at various phases of the project as understanding the process and optimizing the equipment, for process control and for troubleshooting in case of malfunction etc. The main challenge in measuring dose for flue gas applications is that the medium being irradiated is gaseous. Two general approaches for dose measurements are: adding/placing some dosimeters in the reaction vessel (gas) and using the components of the gas itself as a dosimeter. Various techniques and methods have been tried which are discussed in this paper. (author)

  4. Polarized gas targets in electron rings

    The feasibility of performing electron scattering experiments with polarized targets in electron storage rings is discussed. Three examples of the physics which would be accessible with this novel method are given. It is noted that this new method is compatible with recent proposals for linac-stretcher-ring accelerator designs. A new method of producing a polarized hydrogen or deuterium target is proposed and some preliminary results are described. A brief summary of laser-driven polarized targets as well as conventionally-produced polarized atomic beams is included

  5. Seismic time-lapse monitoring of potential gas hydrate dissociation around boreholes : could it be feasible? A conceptual 2D study linking geomechanical and seismic FD models

    Pecher, I.; Yang, J.; Anderson, R.; Tohidi, B.; MacBeth, C. [Heriot-Watt Univ., Edinburgh (United Kingdom). Inst. of Petroleum Engineering; Freij-Ayoub, R.; Clennell, B. [CSIRO Petroleum, Bentley, WA (Australia)

    2008-07-01

    Dissociation of gas hydrate to water and potentially overpressured gas around boreholes may pose a hazard for deep-water hydrocarbon production. Strategies to mitigate this risk include monitoring for early detection of dissociation. Seismic methods are especially promising, primarily because of a high sensitivity of P-wave velocity to gas in the pore space of unconsolidated sediments. This paper presented a study that applied commonly used rock physics modeling to predict the seismic response to gas hydrate dissociation with a focus on P-impedance and performed sensitivity tests. The geomechanical model was translated into seismic models. In order to determine which parameters needed to be particularly well calibrated in experimental and modeling studies, the sensitivity of seismic properties to a variation of input parameters was estimated. The seismic response was predicted from dissociating gas hydrates using two-dimensional finite-difference wave-propagation modeling to demonstrate that despite the small predicted lateral extent of hydrate dissociation, its pronounced effect on seismic properties should allow detection with a seismic source on a drilling platform and receivers on the seafloor. The paper described the methods, models, and results of the study. It was concluded that the key factors for predicting the seismic response of sediments to hydrate dissociation were the mode of gas hydrate distribution, gas distribution in the sediments, gas saturation, and pore pressure. 33 refs., 3 tabs., 8 figs.

  6. Renormalization of Fermi Velocity in a Composite Two Dimensional Electron Gas

    Weger, M.; Burlachkov, L.

    We calculate the self-energy Σ(k, ω) of an electron gas with a Coulomb interaction in a composite 2D system, consisting of metallic layers of thickness d ≳ a0, where a0 = ħ2ɛ1/me2 is the Bohr radius, separated by layers with a dielectric constant ɛ2 and a lattice constant c perpendicular to the planes. The behavior of the electron gas is determined by the dimensionless parameters kFa0 and kFc ɛ2/ɛ1. We find that when ɛ2/ɛ1 is large (≈5 or more), the velocity v(k) becomes strongly k-dependent near kF, and v(kF) is enhanced by a factor of 5-10. This behavior is similar to the one found by Lindhard in 1954 for an unscreened electron gas; however here we take screening into account. The peak in v(k) is very sharp (δk/kF is a few percent) and becomes sharper as ɛ2/ɛ1 increases. This velocity renormalization has dramatic effects on the transport properties; the conductivity at low T increases like the square of the velocity renormalization and the resistivity due to elastic scattering becomes temperature dependent, increasing approximately linearly with T. For scattering by phonons, ρ ∝ T2. Preliminary measurements suggest an increase in vk in YBCO very close to kF.

  7. 2D solar modeling

    Ventura, P; Li, L; Sofia, S; Basu, S; Demarque, P

    2009-01-01

    Understanding the reasons of the cyclic variation of the total solar irradiance is one of the most challenging targets of modern astrophysics. These studies prove to be essential also for a more climatologic issue, associated to the global warming. Any attempt to determine the solar components of this phenomenon must include the effects of the magnetic field, whose strength and shape in the solar interior are far from being completely known. Modelling the presence and the effects of a magnetic field requires a 2D approach, since the assumption of radial symmetry is too limiting for this topic. We present the structure of a 2D evolution code that was purposely designed for this scope; rotation, magnetic field and turbulence can be taken into account. Some preliminary results are presented and commented.

  8. Vertical 2D Heterostructures

    Lotsch, Bettina V.

    2015-07-01

    Graphene's legacy has become an integral part of today's condensed matter science and has equipped a whole generation of scientists with an armory of concepts and techniques that open up new perspectives for the postgraphene area. In particular, the judicious combination of 2D building blocks into vertical heterostructures has recently been identified as a promising route to rationally engineer complex multilayer systems and artificial solids with intriguing properties. The present review highlights recent developments in the rapidly emerging field of 2D nanoarchitectonics from a materials chemistry perspective, with a focus on the types of heterostructures available, their assembly strategies, and their emerging properties. This overview is intended to bridge the gap between two major—yet largely disjunct—developments in 2D heterostructures, which are firmly rooted in solid-state chemistry or physics. Although the underlying types of heterostructures differ with respect to their dimensions, layer alignment, and interfacial quality, there is common ground, and future synergies between the various assembly strategies are to be expected.

  9. Electron transfer in gas surface collisions

    In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

  10. Proton cooling in ultracold low-density electron gas

    Bobrov, A. A.; Bronin, S. Y.; Manykin, E. A.; Zelener, B. B.; Zelener, B. V.; Khikhlukha, D. R.

    2015-11-01

    A sole proton energy loss processes in an electron gas and the dependence of these processes on temperature and magnetic field are studied using molecular dynamics techniques in present work. It appears that for electron temperatures less than 100 K many body collisions affect the proton energy loss and these collisions must be taken into account. The influence of a strong magnetic field on the relaxation processes is also considered in this work. Calculations were performed for electron densities 10 cm-3, magnetic field 1-3 Tesla, electron temperatures 10-50 K, initial proton energies 100-10000 K.

  11. Electron behaviour in CH4/H2 gas mixture in electron-assisted chemical vapour deposition

    Dong Li-Fang; Ma Bo-Qin; Wang Zhi-Jun

    2004-01-01

    The behaviour of electrons in CH4/H2 gas mixture in electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron drift velocity in gas mixture is obtained over a wide range of E/P (the ratio of the electric field to gas pressure) from 1500 to 300000 (V/m kPa-1). The electron energy distribution and average energy under different gas pressure (0.1-20kPa) and CH4 concentration (0.5%-10.0%) are calculated. Their effects on the diamond growth are also discussed. It is believed that these results will be helpful to the selection of optimum experimental conditions for high quality diamond film deposition.

  12. New "wet type" electron beam flue gas treatment pilot plant

    Tan, Erdal; Ünal, Suat; Doğan, Alişan; Letournel, Eric; Pellizzari, Fabien

    2016-02-01

    We describe a new pilot plant for flue gas cleaning by a high energy electron beam. The special feature of this pilot plant is a uniquely designed reactor called VGS® (VIVIRAD Gas Scrubber, patent pending), that allows oxidation/reduction treating flue gas in a single step. The VGS® process combines a scrubber and an advanced oxidation/reduction process with the objective of optimizing efficiency and treatment costs of flue gas purification by electron accelerators. Promising treatment efficiency was achieved for SOx and NOx removal in early tests (99.2% and 80.9% respectively). The effects of various operational parameters on treatment performance and by-product content were investigated during this study.

  13. Transport of a relativistic electron beam through hydrogen gas

    In this thesis the author describes the transport properties of an electron beam through vacuum and through hydrogen gas with pressure ranging from 25 to 1000 Pa. Maximum beam energy and current are 0.8 MeV and 6 kA, respectively. The pulse length is around 150 ns. A description is given of the experimental device. Also the diagnostics for probing the beam and the plasma, produced by the beam, are discussed, as well as the data acquisition system. The interaction between the beam and hydrogen gas with a pressure around 200 Pa is considered. A plasma with density around 1019 m-3 is produced within a few nanoseconds. Measurements yield the atomic hydrogen temperature, electron density, beam energy loss, and induced plasma current and these are compared with the results of a model combining gas ionization and dissociation, and turbulent plasma heating. The angular distribution of the beam electrons about the magnetic field axis is discussed. (Auth.)

  14. Experimental investigation of fast electron transport in solid density matter: Recent results from a new technique of X-ray energy-encoded 2D imaging

    Labate, L.; Förster, E.; Giulietti, A.; Giulietti, D.; Höfer, S.; Kämpfer, T.; Köster, P.; Kozlová, Michaela; Levato, T.; Lötzsch, R.; Lübecke, A.; Mocek, Tomáš; Polan, Jiří; Rus, Bedřich; Uschmann, I.; Zamponi, F.; Gizzi, L.A.

    2009-01-01

    Roč. 27, č. 4 (2009), s. 643-649. ISSN 0263-0346 R&D Projects: GA MŠk(CZ) 7E09092 Grant ostatní: TUIXS(XE) FP6-NEST No.12843 Institutional research plan: CEZ:AV0Z10100523 Keywords : anisotropic Bremsstrahlung * fast electron diagnostics * fast electron transport * high-density matter * relativistic electrons Subject RIV: BH - Optics, Masers, Lasers Impact factor: 4.420, year: 2008

  15. Thermoelectric instability of electron-hole gas in semiconductors

    It is shown that thermoelectric instability is possible in a solid semiconductor in electron-hole gas by heating. The dissipation relaxation mechanism is capable of quenching the excitation. The anisotropy, corresponding to the high values of the gas characteristics in the direction concurrent with the heatup direction, facilitates the origination of cellular motion. The criteria of excitation and the cell dimensions ratios at the moment of its origination are defined. Possible experiments are considered and evaluations are carried out. 10 refs

  16. Implementing the GISB standards in Canada - electronic gas trading

    Standards promulgated by the Gas Industry Standards Board (GISB) in the United States, its objective and applicability in Canada are discussed. The standards, while sponsored by an American trade organization, have had significant Canadian input, and are considered applicable throughout North America, although implementation in Canada is voluntary. In developing the standards, the intent of the GISB was to developing business practice and electronic commerce standards for the natural gas industry. Despite voluntary application in Canada, Canadians are affected by the standards since some 50 per cent of Canadian gas is exported to U.S. consumers, and U.S. gas is imported for Canadian consumers in certain parts of the country. In actual fact. a Canadian GISB Implementation Task Force has been established to develop recommendations for Canadian implementation. The task force is broadly representative of the industry and published its report in March of 1997. It explains the nature of the standards and provides details about the definition of 'gas day' , nomination schedules, accounting issues, electronic delivery mechanisms, capacity release, standard unit of measure for nominations, confirmations, scheduling, measurement reports and invoicing. Questions regarding electronic contracting and enforceability of electronic contracts also have been reviewed. Details are currently under consideration by a Working Group. Status of contracts under the Statute of Frauds, the Evidence Act and the Interpretation Act is reviewed, and legislative requirements in Canada to make electronic commerce legally enforceable are outlined. At present electronic transactions would likely be enforceable provided they are preceded by a paper-based Electronic Commerce Trading Partner Agreement

  17. Calibration of an Electronic Radon Gas Personnel Dosimeter

    Full text: The monitoring of radon exposure at working places is of great importance. Up to now passive measurement systems for the registration of radon gas were used. Recently an Electronic Radon Gas Personal Dosimeter as an active measurement system for the registration of the radon exposure came into the market (DOSEman; Sarad GmbH, Dresden, Germany) In this personal monitor the radon gas diffuses through a membrane into a measurement chamber. A silicon detector system records spectroscopically the alpha decays of the radon gas and of the short-lived progeny 218Po and 214Po gathered onto the detector by an electrical field. The calibration was tested and the following parameters specified for this equipment were checked: diffusion behaviour of the radon gas into the measurement chamber, susceptibility to thoron, efficiency, influence of humidity, accuracy and the detection limit. (author)

  18. Characterisation of an electronic radon gas personal dosemeter

    The monitoring of radon exposure at workplaces is of great importance. Up to now passive measurement systems have been used for the registration of radon gas. Recently an electronic radon gas personal dosemeter came onto the market as an active measurement system for the registration of radon exposure (DOSEman; Sarad GmbH, Dresden, Germany). In this personal monitor, the radon gas diffuses through a membrane into a measurement chamber. A silicon detector system records spectroscopically the alpha decays of the radon gas and of the short-lived progeny 218Po and 214Po gathered onto the detector by an electrical field. In this work the calibration was tested and a proficiency test of this equipment was made. The diffusion behaviour of the radon gas into the measurement chamber, susceptibility to thoron, influence of humidity, accuracy and the detection limit were checked. (author)

  19. Pulsed electron beam propagation in argon and nitrogen gas mixture

    The paper presents the results of current measurements for the electron beam, propagating inside a drift tube filled in with a gas mixture (Ar and N2). The experiments were performed using the TEA-500 pulsed electron accelerator. The main characteristics of electron beam were as follows: 60 ns pulse duration, up to 200 J energy, and 5 cm diameter. The electron beam propagated inside the drift tube assembled of three sections. Gas pressures inside the drift tube were 760 ± 3, 300 ± 3, and 50 ± 1 Torr. The studies were performed in argon, nitrogen, and their mixtures of 33%, 50%, and 66% volume concentrations, respectively

  20. Edge spin accumulation in a two-dimensional electron gas with two subbands

    Khaetskii, Alexander; Egues, J. Carlos

    We have studied the edge spin accumulation in 2D electron gas due to the intrinsic mechanism of spin-orbit interaction for the case of a two-subband structure. This study is strongly motivated by recent experiments which observed the spin accumulation near the edges of a high mobility 2D electron system in a bilayer symmetric GaAs structure in contrast to zero effect in a single-layer configuration. Our theoretical explanation is based on the Rashba-like spin-orbit interaction which arises as a result of the coupling between two subband states of opposite parities in a symmetric quantum well. Following the method developed in, we have calculated the edge spin density in a quasi-ballistic regime, and explained the experimental results, in particular, a large magnitude of the edge spin density. We showed that one can easily proceed from the regime of strong spin accumulation to the regime of weak one. It opens up a possibility to construct an interesting new spintronic device Supported by FAPESP (Brazil).

  1. c2d Spitzer IRS spectra of disks around T Tauri stars. III. [Ne II], [Fe I], and H-2 gas-phase lines

    Lahuis, Fred; van Dishoeck, Ewine F.; Blake, Geoffrey A.; Evans, Neal J.; Kessler-Silacci, Jacqueline E.; Pontoppidan, Klaus M.

    2007-01-01

    We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low-mass pre-main-sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [ Ne II] and [ Fe I] toward classical T Tauri stars in similar to 20% and similar

  2. Gas-discharge electron tube with beam extraction into mean-pressure gas

    Gitt, V.D.; Noskov, D.A.; Orlikov, L.N.; Ryltsev, P.I.; Tikhomirov, S.I.; Chikin, E.V. (Tomskij Inst. Avtomatizirovannykh Sistem Upravleniya i Radioehlektroniki (USSR))

    Described is an electron gun on the base of high-voltage glow supplied with a gas-dynamical window for electron beam extraction into gas 10/sup 3/-10/sup 5/ Pa. The gun discharge system comprises cold aluminium cathode and sectional anode formed by three copper disks with axial holes. The gun is intended for operation in a continuous mode at accelerating voltage up to 60 kV and 30 mA discharge current as well as for experimental investigations of electron beam scattering at average pressure. Measurements of current density distribution by cross section of extracted beams are conducted and images of gas ionization zones are taken by 20-60 keV electron beam at nitrogen pressure 1.3-2 kPa.

  3. Gas-discharge electron tube with beam extraction into mean-pressure gas

    Described is an electron gun on the base of high-voltage glow supplied with a gas-dynamical window for electron beam extraction into gas 103-105 Pa. The gun discharge system comprises cold aluminium cathode and sectional anode formed by three copper disks with axial holes. The gun is intended for operation in a continuous mode at accelerating voltage up to 60 kV and 30 mA discharge current as well as for experimental investigations of electron beam scattering at average pressure. Measurements of current density distribution by cross section of extracted beams are conducted and images of gas ionization zones are taken by 20-60 keV electron beam at nitrogen pressure 1.3-2 kPa

  4. Electron beam treatment of coal-fired flue gas

    The removal of SOX and NOX by electron beam irradiation from simulated coal-fired flue gas was studied using a small scale flow system (0.9 Nm3/hr) to get basic data for forthcoming pilot scale test in Japan. The standard concentrations of the gas components were NO: 150 ppm, SO2: 500 ppm, O2: 6%, H2O: 12% ('wet base'), N2: balance. Gaseous HN3 (1035-1150 ppm) was added to the simulated flue gas. The gas was irradiated with an electron beam (1.5 MeV) from a Cockcroft-Walton type electron accelerator. The irradiation vessel with three irradiation chambers was used in order to investigate the effect of multiple irradiation by comparing the effect of single, double and triple irradiations. The standard gas temperature in the system was set to be 650degC. The SOX removal was increased at low temperature. The increasing efficiency of NOX removal by multiple irradiation was observed. Reaction mechanism of NOX and SO2 removals is also discussed. The target SOX and NOX removal ratios (94% and 80%, respectively) and low leaked NH3 (less than 10 ppm) were achieved at 8 kGy. (author)

  5. The Gas Electron Multiplier Chamber Exhibition LEPFest 2000

    2000-01-01

    The Gas Electron Multiplier (GEM) is a novel device introduced in 1996.Large area detectors based on this technology are in construction for high energy physics detectors.This technology can also be used for high-rate X-ray imaging in medical diagnostics and for monitoring irradiation during cancer treatment

  6. Pilot plant for electron beam flue gas treatment

    Double stage gas irradiation (2 electron accelerators, 50 kW/700 keV each) is the main technological principle employed in the Polish pilot plant (20,000 Nm3/h) constructed at EPS Kaweczyn (low/medium sulphur coal). The pilot plant design is described in this paper. (author)

  7. Small angle elastic scattering of electrons by noble gas atoms

    In this thesis, measurements are carried out to obtain small angle elastic differential cross sections in order to check the validity of Kramers-Kronig dispersion relations for electrons scattered by noble gas atoms. First, total cross sections are obtained for argon, krypton and xenon. Next, a parallel plate electrostatic energy analyser for the simultaneous measurement of doubly differential cross section for small angle electron scattering is described. Also absolute differential cross sections are reported. Finally the forward dispersion relation for electron-helium collisions is dealt with. (Auth.)

  8. Electron cloud sizes in gas-filled detectors

    Electron cloud sizes have been calculated for gas mixtures containing Ar, Xe, CO2, CH4, and N2 for drifts through a constant electric field. The transport coefficients w and D/μ are in good agreement with experimental data of various sources for pure gases. Results of measurements, also performed in this work, for Ar+CO2, Ar+CH4, and Ar+Xe+CO2 mixtures are in fair agreement with the calculated cloud sizes. For a large number of useful gas mixtures calculated electron cloud sizes are presented and discussed, most of which are given for the first time. A suggestion is made for an optimal gas mixture for an X-ray position sensitive proportional counter for medium and low energies. (orig.)

  9. Development of electron beam flue gas treatment technology

    Smoke treatment system making use of electron beam irradiation made it possible to simultaneously eliminate SOx and NOn from exhaust gas. The fundamental study of the system was started in the seventies and at present, its application in practical use is under way. A pilot plant for the smoke treatment system was constructed in cooperation of Chubu Electric Power Company, Inc., Japan Atomic Energy Research Institute and Ebara Corporation and several tests with the actual exhaust gas were conducted during the period, Oct. 1992-Dec. 1993 and the treatment efficiency and the control capacity of this system was confirmed to be so high as the conventional systems and many engineering data were obtained. A high treatment efficiency (>94% for desulfurization and >80% for denitrification) was obtainable by choosing the optimum irradiation amount of electron beam and the optimum temperature of gas to treat. And this system was found superior from a financial aspect to the conventional smoke treatment system. (M.N.)

  10. Electronic structure of charge-density-wave state in quasi-2D KMo6O17 purple bronze characterized by angle resolved photoemission spectroscopy

    Valbuena, M. A.; Avila, J.; Drouard, S.; Guyot, H.; Asensio, M. C.

    2006-01-01

    We report on an angle-resolved-photoemission spectroscopy (ARPES) investigation of layered quasi-two dimensional (2D) Molybdenum purple bronze KMo6O17 in order to study and characterizes the transition to a charge-density-wave (CDW) state. We have performed photoemission temperature dependent measurements cooling down from room temperature (RT) to 32 K, well below the Peierls transition for this material, with CDW transition temperature Tc =110 K. The spectra have been taken at a selected kF point of the Fermi surface (FS) that satisfies the nesting condition of the FS, looking for the characteristic pseudo-gap opening in this kind of materials. The pseudogap has been estimated and it result to be in agreement with our previous works. The shift to lower binding energy of crossing Fermi level ARPES feature have been also confirmed and studied as a function of temperature, showing a rough like BCS behaviour. Finally we have also focused on ARPES measurements along ΓM¯ high symmetry direction for both room and low temperature states finding some insight for ‘shadow’ or back folded bands indicating the new periodicity of real lattice after the CDW lattice distortion.