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Sample records for 2d electron gas

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

    Energy Technology Data Exchange (ETDEWEB)

    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. Analysis of homogeneity of 2D electron gas at decreasing of electron density

    OpenAIRE

    Sherstobitov, A. A.; Minkov, G. M.; Germanenko, A. V.; Rut, O. E.; Soldatov, I. V.; Zvonkov, B. N.

    2010-01-01

    We investigate the gate voltage dependence of capacitance of a system gate - 2D electron gas (C-Vg). The abrupt drop of capacitance at decreasing concentration was found. The possible reasons of this drop, namely inhomogeneity of electron density distribution and serial resistance of 2D electron gas are discussed. Simultaneous analysis of gate voltage dependences of capacitance and resistance has shown that in heavily doped 2D systems the main role in the drop of capacitance at decreasing con...

  3. Coulomb scattering in a 2D interacting electron gas and production of EPR pairs.

    Science.gov (United States)

    Saraga, D S; Altshuler, B L; Loss, Daniel; Westervelt, R M

    2004-06-18

    We propose a setup to generate nonlocal spin Einstein-Podolsky-Rosen pairs via pair collisions in a 2D interacting electron gas, based on constructive two-particle interference in the spin-singlet channel at the pi/2 scattering angle. We calculate the scattering amplitude via the Bethe-Salpeter equation in the ladder approximation and small r(s) limit and find that the Fermi sea leads to a substantial renormalization of the bare scattering process. From the scattering length, we estimate the current of spin-entangled electrons and show that it is within experimental reach.

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

    Science.gov (United States)

    Sinner, Andreas; Ziegler, Klaus

    2016-08-03

    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 [Formula: see text].

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

    CERN Document Server

    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.

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

    Science.gov (United States)

    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 .

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

    Science.gov (United States)

    Cantoni, Claudia; Gazquez, Jaume; Miletto Granozio, Fabio; Oxley, Mark P; Varela, Maria; Lupini, Andrew R; Pennycook, Stephen J; Aruta, Carmela; di Uccio, Umberto Scotti; Perna, Paolo; Maccariello, Davide

    2012-08-02

    Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial electron density and system polarization are crucial for establishing the highly debated origin of the 2D electron gas. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Magnetoresistance of a 2D electron gas caused by electron interactions in the transition from the diffusive to the ballistic regime.

    Science.gov (United States)

    Li, L; Proskuryakov, Y Y; Savchenko, A K; Linfield, E H; Ritchie, D A

    2003-02-21

    On a high-mobility 2D electron gas we have observed, in strong magnetic fields (omega(c)tau>1), a parabolic negative magnetoresistance caused by electron-electron interactions in the regime of k(B)Ttau/ variant Planck's over 2pi approximately 1, which is the transition from the diffusive to the ballistic regime. From the temperature dependence of this magnetoresistance the interaction correction to the conductivity deltasigma(ee)(xx)(T) is obtained in the situation of a long-range fluctuation potential and strong magnetic field. The results are compared with predictions of the new theory of interaction-induced magnetoresistance.

  9. Magnetoresistance of a 2D electron gas caused by electron interactions in the transition from the diffusive to the ballistic regime

    OpenAIRE

    Li, L.; Proskuryakov, Y. Y.; Savchenko, A. K.; Linfield, E.H.; Ritchie, D. A.

    2002-01-01

    On a high-mobility 2D electron gas we have observed, in strong magnetic fields (omega_{c} tau > 1), a parabolic negative magnetoresistance caused by electron-electron interactions in the regime of k_{B} T tau / hbar ~ 1, which is the transition from the diffusive to the ballistic regime. From the temperature dependence of this magnetoresistance the interaction correction to the conductivity delta sigma_{xx}^{ee}(T) is obtained in the situation of a long-range fluctuation potential and strong ...

  10. Gas sensing in 2D materials

    Science.gov (United States)

    Yang, Shengxue; Jiang, Chengbao; Wei, Su-huai

    2017-06-01

    Two-dimensional (2D) layered inorganic nanomaterials have attracted huge attention due to their unique electronic structures, as well as extraordinary physical and chemical properties for use in electronics, optoelectronics, spintronics, catalysts, energy generation and storage, and chemical sensors. Graphene and related layered inorganic analogues have shown great potential for gas-sensing applications because of their large specific surface areas and strong surface activities. This review aims to discuss the latest advancements in the 2D layered inorganic materials for gas sensors. We first elaborate the gas-sensing mechanisms and introduce various types of gas-sensing devices. Then, we describe the basic parameters and influence factors of the gas sensors to further enhance their performance. Moreover, we systematically present the current gas-sensing applications based on graphene, graphene oxide (GO), reduced graphene oxide (rGO), functionalized GO or rGO, transition metal dichalcogenides, layered III-VI semiconductors, layered metal oxides, phosphorene, hexagonal boron nitride, etc. Finally, we conclude the future prospects of these layered inorganic materials in gas-sensing applications.

  11. Quantum coherence selective 2D Raman-2D electronic spectroscopy.

    Science.gov (United States)

    Spencer, Austin P; Hutson, William O; Harel, Elad

    2017-03-10

    Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.

  12. 2D hydrodynamic simulations of a variable length gas target for density down-ramp injection of electrons into a laser wakefield accelerator

    Energy Technology Data Exchange (ETDEWEB)

    Kononenko, O., E-mail: olena.kononenko@desy.de [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany); Lopes, N.C.; Cole, J.M.; Kamperidis, C.; Mangles, S.P.D.; Najmudin, Z. [The John Adams Institute for Accelerator Science, The Blackett Laboratory, Imperial College London, SW7 2BZ UK (United Kingdom); Osterhoff, J. [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany); Poder, K. [The John Adams Institute for Accelerator Science, The Blackett Laboratory, Imperial College London, SW7 2BZ UK (United Kingdom); Rusby, D.; Symes, D.R. [Central Laser Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom); Warwick, J. [Queens University Belfast, North Ireland (United Kingdom); Wood, J.C. [The John Adams Institute for Accelerator Science, The Blackett Laboratory, Imperial College London, SW7 2BZ UK (United Kingdom); Palmer, C.A.J. [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany)

    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.

  13. 2D microwave imaging reflectometer electronics

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. Linear in-plane magnetoconductance and spin susceptibility of a 2D electron gas on a vicinal silicon surface

    OpenAIRE

    Proskuryakov, Y. Y.; Kvon, Z. D.; Savchenko, A. K.

    2003-01-01

    In this work we have studied the parallel magnetoresistance of a 2DEG near a vicinal silicon surface. An unusual, linear magnetoconductance is observed in the fields up to $B = 15$ T, which we explain by the effect of spin olarization on impurity scattering. This linear magnetoresistance shows strong anomalies near the boundaries of the minigap in the electron spectrum of the vicinal system.

  15. Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering

    Institute of Scientific and Technical Information of China (English)

    Liang Pang

    2014-01-01

    We theoretically present the intrinsic limits to electron mobility in the modulation-doped AlGaN/GaN two-dimensional electron gas (2DEG) due to effects including acoustic deformation potential (DP) scattering, piezoelectric scattering (PE), and polar-optic phonon scattering (POP). We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.

  16. An unambiguous identification of 2D electron gas features in the photoluminescence spectrum of AlGaN/GaN heterostructures

    Science.gov (United States)

    Jana, Dipankar; Sharma, T. K.

    2016-07-01

    A fast and non-destructive method for probing the true signatures of 2D electron gas (2DEG) states in AlGaN/GaN heterostructures is presented. Two broad features superimposed with interference oscillations are observed in the low temperature photoluminescence (PL) spectrum. The two features are identified as the ground and excited 2DEG states which are confirmed by comparing the PL spectra of as-grown and top barrier layer etched samples. Broad PL features disappear at a certain temperature along with the associated interference oscillations. Furthermore, the two broad PL features depicts specific temperature and excitation intensity dependencies which make them easily distinguishable from the bandedge excitonic or defect related PL features. The presence of strong interference oscillations associated with the 2DEG PL features is explained by considering the localized generation of PL signal at the AlGaN/GaN heterointerface. Finally, a large value of the polarization induced electric field of ~1.01 MV cm-1 is reported from PL measurements for AlGaN/GaN HEMT structures. It became possible only when the true identification of 2DEG features was made possible by the proposed method.

  17. 2D Electron Gas with 100% Spin-Polarization in the (LaMnO 3 ) 2 /(SrTiO 3 ) 2 Superlattice under Uniaxial Strain

    KAUST Repository

    Cossu, Fabrizio

    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.

  18. Scalable Fabrication of 2D Semiconducting Crystals for Future Electronics

    Directory of Open Access Journals (Sweden)

    Jiantong Li

    2015-12-01

    Full Text Available Two-dimensional (2D layered materials are anticipated to be promising for future electronics. However, their electronic applications are severely restricted by the availability of such materials with high quality and at a large scale. In this review, we introduce systematically versatile scalable synthesis techniques in the literature for high-crystallinity large-area 2D semiconducting materials, especially transition metal dichalcogenides, and 2D material-based advanced structures, such as 2D alloys, 2D heterostructures and 2D material devices engineered at the wafer scale. Systematic comparison among different techniques is conducted with respect to device performance. The present status and the perspective for future electronics are discussed.

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

    Energy Technology Data Exchange (ETDEWEB)

    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. First Principles Calculations of Electronic Excitations in 2D Materials

    DEFF Research Database (Denmark)

    Rasmussen, Filip Anselm

    -thin electronics and high efficiency solar cells. Contrary to many other nano-materials, methods for large scale fabrication and patterning have already been demonstrated and the first real technological applications have already be showcased. Still the technology is very young and the number of well-studied 2D...... materials are few. However as the list of 2D materials is growing it is necessary to investigate their fundamental structural, electronic and optical properties. These are determined by the atomic and electronic structure of the materials that can quite accurately predicted by computational quantum...... as if it is being screened by the electrons in the material. This method has been very successful for calculating quasiparticle energies of bulk materials but results have been more varying for 2D materials. The reason is that the 2D confined electrons are less able to screen the added charge and some...

  1. Transport Experiments on 2D Correlated Electron Physics in Semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, Daniel

    2014-03-24

    This research project was designed to investigate experimentally the transport properties of the 2D electrons in Si and GaAs, two prototype semiconductors, in several new physical regimes that were previously inaccessible to experiments. The research focused on the strongly correlated electron physics in the dilute density limit, where the electron potential energy to kinetic energy ratio rs>>1, and on the fractional quantum Hall effect related physics in nuclear demagnetization refrigerator temperature range on samples with new levels of purity and controlled random disorder.

  2. Structures of quantum 2D electron-hole plasmas

    CERN Document Server

    Filinov, V S; Fehske, H; Levashov, P R; Fortov, V E

    2008-01-01

    We investigate structures of 2D quantum electron-hole (e-h) plasmas by the direct path integral Monte Carlo method (PIMC) in a wide range of temperature, density and hole-to-electron mass ratio. Our simulation includes a region of appearance and decay of the bound states (excitons and biexcitons), the Mott transition from the neutral e-h plasma to metallic-like clusters, formation from clusters the hexatic-like liquid and formation of the crystal-like lattice.

  3. Optimizing sparse sampling for 2D electronic spectroscopy

    Science.gov (United States)

    Roeding, Sebastian; Klimovich, Nikita; Brixner, Tobias

    2017-02-01

    We present a new data acquisition concept using optimized non-uniform sampling and compressed sensing reconstruction in order to substantially decrease the acquisition times in action-based multidimensional electronic spectroscopy. For this we acquire a regularly sampled reference data set at a fixed population time and use a genetic algorithm to optimize a reduced non-uniform sampling pattern. We then apply the optimal sampling for data acquisition at all other population times. Furthermore, we show how to transform two-dimensional (2D) spectra into a joint 4D time-frequency von Neumann representation. This leads to increased sparsity compared to the Fourier domain and to improved reconstruction. We demonstrate this approach by recovering transient dynamics in the 2D spectrum of a cresyl violet sample using just 25% of the originally sampled data points.

  4. 2D-MoO3 nanosheets for superior gas sensors

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Science.gov (United States)

    Cho, Byungjin; Yoon, Jongwon; Lim, Sung Kwan; Kim, Ah Ra; Choi, Sun-Young; Kim, Dong-Ho; Lee, Kyu Hwan; Lee, Byoung Hun; Ko, Heung Cho; Hahm, Myung Gwan

    2015-09-25

    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.

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

    Science.gov (United States)

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

    2008-09-07

    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.

  8. Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics.

    Science.gov (United States)

    Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios

    2016-10-31

    In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.

  9. Electron-Phonon Scattering in Atomically Thin 2D Perovskites.

    Science.gov (United States)

    Guo, Zhi; Wu, Xiaoxi; Zhu, Tong; Zhu, Xiaoyang; Huang, Libai

    2016-11-22

    Two-dimensional (2D) atomically thin perovskites with strongly bound excitons are highly promising for optoelectronic applications. However, the nature of nonradiative processes that limit the photoluminescence (PL) efficiency remains elusive. Here, we present time-resolved and temperature-dependent PL studies to systematically address the intrinsic exciton relaxation pathways in layered (C4H9NH3)2(CH3NH3)n-1PbnI3n+1 (n = 1, 2, 3) structures. Our results show that scatterings via deformation potential by acoustic and homopolar optical phonons are the main scattering mechanisms for excitons in ultrathin single exfoliated flakes, exhibiting a T(γ) (γ = 1.3 to 1.9) temperature dependence for scattering rates. We attribute the absence of polar optical phonon and defect scattering to efficient screening of Coulomb potential, similar to what has been observed in 3D perovskites. These results establish an understanding of the origins of nonradiative pathways and provide guidelines for optimizing PL efficiencies of atomically thin 2D perovskites.

  10. Optical Signatures from Magnetic 2-D Electron Gases in High Magnetic Fields to 60 Tesla

    Energy Technology Data Exchange (ETDEWEB)

    Crooker, S.A.; Kikkawa, J.M.; Awschalom, D.D.; Smorchikova, I.P.; Samarth, N.

    1998-11-08

    We present experiments in the 60 Tesla Long-Pulse magnet at the Los Alamos National High Magnetic Field Lab (NHMFL) focusing on the high-field, low temperature photoluminescence (PL) from modulation-doped ZnSe/Zn(Cd,Mn)Se single quantum wells. High-speed charge-coupled array detectors and the long (2 second) duration of the magnet pulse permit continuous acquisition of optical spectra throughout a single magnet shot. High-field PL studies of the magnetic 2D electron gases at temperatures down to 350mK reveal clear intensity oscillations corresponding to integer quantum Hall filling factors, from which we determine the density of the electron gas. At very high magnetic fields, steps in the PL energy are observed which correspond to the partial unlocking of antiferromagnetically bound pairs of Mn2+ spins.

  11. Conductivity magnetooscillations in 2D electron-impurity system under microwave irradiation: role of magnetoplasmons

    OpenAIRE

    Takhtamirov, E. E.; V. A. Volkov

    2005-01-01

    It is developed a many-electron approach to explain the recently observed conductivity magnetooscillations in very high mobility 2D electron systems under microwave irradiation. For the first time a theory takes into account the microwave-induced renormalization of the screened impurity potential. As a result this potential has singular, dynamic and non-linear in electric field nature. That changes the picture of scattering of electrons at impurities in a ``clean'' 2D system essentially: for ...

  12. Dual-mode operation of 2D material-base hot electron transistors

    KAUST Repository

    Lan, Yann-Wen

    2016-09-01

    Vertical hot electron transistors incorporating atomically-thin 2D materials, such as graphene or MoS2, in the base region have been proposed and demonstrated in the development of electronic and optoelectronic applications. To the best of our knowledge, all previous 2D material-base hot electron transistors only considered applying a positive collector-base potential (V-CB > 0) as is necessary for the typical unipolar hot-electron transistor behavior. Here we demonstrate a novel functionality, specifically a dual-mode operation, in our 2D material-base hot electron transistors (e.g. with either graphene or MoS2 in the base region) with the application of a negative collector-base potential (V-CB < 0). That is, our 2D material-base hot electron transistors can operate in either a hot-electron or a reverse-current dominating mode depending upon the particular polarity of VCB. Furthermore, these devices operate at room temperature and their current gains can be dynamically tuned by varying VCB. We anticipate our multi-functional dual-mode transistors will pave the way towards the realization of novel flexible 2D material-based high-density and low-energy hot-carrier electronic applications.

  13. 2D Optical Streaking for Ultra-Short Electron Beam Diagnostics

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Y.T.; Huang, Z.; Wang, L.; /SLAC

    2011-12-14

    field ionization, which occurs in plasma case, gases species with high field ionization threshold should be considered. For a linear polarized laser, the kick to the ionized electrons depends on the phase of the laser when the electrons are born and the unknown timing jitter between the electron beam and laser beam makes the data analysis very difficult. Here we propose to use a circular polarized laser to do a 2-dimensional (2D) streaking (both x and y) and measure the bunch length from the angular distribution on the screen, where the phase jitter causes only a rotation of the image on the screen without changing of the relative angular distribution. Also we only need to know the laser wavelength for calibration. A similar circular RF deflecting mode was used to measure long bunches. We developed a numerical particle-in-Cell (PIC) code to study the dynamics of ionization electrons with the high energy beam and the laser beam.

  14. Fermi-to-Bose crossover in a trapped quasi-2D gas of fermionic atoms

    Science.gov (United States)

    Turlapov, A. V.; Kagan, M. Yu

    2017-09-01

    The physics of many-body systems where particles are restricted to move in two spatial dimensions is challenging and even controversial: on one hand, neither long-range order nor Bose condensation may appear in infinite uniform 2D systems at finite temperature, on the other hand this does not prohibit superfluidity or superconductivity. Moreover, 2D superconductors, such as cuprates, are among the systems with the highest critical temperatures. Ultracold atoms are a platform for studying 2D physics. Unique from other physical systems, quantum statistics may be completely changed in an ultracold gas: an atomic Fermi gas may be smoothly crossed over into a gas of Bose molecules (or dimers) by tuning interatomic interactions. We review recent experiments where such crossover has been demonstrated, as well as critical phenomena in the Fermi-to-Bose crossover. We also present simple theoretical models describing the gas at different points of the crossover and compare the data to these and more advanced models.

  15. Theoretical studies on electronic structure and x-ray spectroscopies of 2D materials

    OpenAIRE

    2016-01-01

    Extraordinary chemical and physical properties have been discovered from the studies of two-dimensional (2D) materials, ever since the successful exfoliation of graphene, the first 2D material. Theoretical investigations of electronic structure and spectroscopies of these materials play a fundamental role in deep understanding the various properties. In particular, the band structure and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy can provide critical information near the ...

  16. The uniform electron gas

    CERN Document Server

    Loos, Pierre-François

    2016-01-01

    The uniform electron gas or UEG (also known as jellium) is one of the most fundamental models in condensed-matter physics and the cornerstone of the most popular approximation --- the local-density approximation --- within density-functional theory. In this article, we provide a detailed review on the energetics of the UEG at high, intermediate and low densities, and in one, two and three dimensions. We also report the best quantum Monte Carlo and symmetry-broken Hartree-Fock calculations available in the literature for the UEG and discuss the phase diagrams of jellium.

  17. Preparation of 2D crystals of membrane proteins for high-resolution electron crystallography data collection.

    Science.gov (United States)

    Abeyrathne, Priyanka D; Chami, Mohamed; Pantelic, Radosav S; Goldie, Kenneth N; Stahlberg, Henning

    2010-01-01

    Electron crystallography is a powerful technique for the structure determination of membrane proteins as well as soluble proteins. Sample preparation for 2D membrane protein crystals is a crucial step, as proteins have to be prepared for electron microscopy at close to native conditions. In this review, we discuss the factors of sample preparation that are key to elucidating the atomic structure of membrane proteins using electron crystallography.

  18. Evolution of Matter Wave Interference of Bose-Condensed Gas in a 2D Optical Lattice

    Institute of Scientific and Technical Information of China (English)

    XUZhi-Jun; LINGuo-Cheng; XUJun; LIZhen

    2005-01-01

    We investigate the average particle-number distribution of the atoms in the combined potential of 2D optical lattices and 31) harmonic magnetic trap based on the Gross-Pitaevskii equation. After the combined potential is switched of[, and only the optical lattice is switched off, we give the analytical results of the wavefunction of the Bosecondensed gas at any time t by using a propagator method. For both disk-shaped and cigar-shaped Bose-condensed gas,we discuss the evolution process of the central and side peaks of the interference pattern.

  19. Uniform quantized electron gas

    Science.gov (United States)

    Høye, Johan S.; Lomba, Enrique

    2016-10-01

    In this work we study the correlation energy of the quantized electron gas of uniform density at temperature T  =  0. To do so we utilize methods from classical statistical mechanics. The basis for this is the Feynman path integral for the partition function of quantized systems. With this representation the quantum mechanical problem can be interpreted as, and is equivalent to, a classical polymer problem in four dimensions where the fourth dimension is imaginary time. Thus methods, results, and properties obtained in the statistical mechanics of classical fluids can be utilized. From this viewpoint we recover the well known RPA (random phase approximation). Then to improve it we modify the RPA by requiring the corresponding correlation function to be such that electrons with equal spins can not be on the same position. Numerical evaluations are compared with well known results of a standard parameterization of Monte Carlo correlation energies.

  20. Local Probing of Phase Coherence in a Strongly Interacting 2D Quantum Gas

    Science.gov (United States)

    Luick, Niclas; Siegl, Jonas; Hueck, Klaus; Morgener, Kai; Lompe, Thomas; Weimer, Wolf; Moritz, Henning

    2016-05-01

    The dimensionality of a quantum system has a profound impact on its coherence and superfluid properties. In 3D superfluids, bosonic atoms or Cooper pairs condense into a macroscopic wave function exhibiting long-range phase coherence. Meanwhile, 2D superfluids show a strikingly different behavior: True long-range coherence is precluded by thermal fluctuations, nevertheless Berezinskii-Kosterlitz-Thouless (BKT) theory predicts that 2D systems can still become superfluid. The superfluid state is characterized by an algebraic decay of phase correlations g1(r) ~r - τ / 4 , where the decay exponent τ is directly related to the superfluid density ns according to τ = 4 /(nsλdB2) . I will present local coherence measurements in a strongly interacting 2D gas of diatomic 6 Li molecules. A self-interference technique allows us to locally extract the algebraic decay exponent and to reconstruct the superfluid density. We determine the scaling of the decay exponent with phase space density to provide a benchmark for studies of 2D superfluids in the strongly interacting regime.

  1. The ionized gas in the central region of NGC 5253: 2D mapping of the physical and chemical properties

    CERN Document Server

    Monreal-Ibero, Ana; Vilchez, Jose M

    2012-01-01

    ABRIDGED: NGC5253 was previously studied by our group with the aim to elucidate in detail the starburst interaction processes. Some open issues regarding the 2D structure of the main properties of the ionized gas remain to be addressed. Using IFS data obtained with FLAMES, we derived 2D maps for different tracers of electron density (n_e), electron temperature (T_e) and ionization degree. The maps for n_e as traced by several line ratios are compatible with a 3D stratified view of the nebula with the highest n_e in the innermost layers and a decrease of n_e outwards. To our knowledge, this is the first time that a T_e map based on [SII] lines for an extragalactic object is presented. The joint interpretation of our two T_e maps is consistent with a T_e structure in 3D with higher temperatures close to the main ionizing source surrounded by a colder and more diffuse component. The highest ionization degree is found at the peak of emission for the gas with relatively high ionization in the main GHIIR and lower ...

  2. Coherent-pulse 2D crystallography using a free-electron laser x-ray source.

    Science.gov (United States)

    Mancuso, A P; Schropp, A; Reime, B; Stadler, L-M; Singer, A; Gulden, J; Streit-Nierobisch, S; Gutt, C; Grübel, G; Feldhaus, J; Staier, F; Barth, R; Rosenhahn, A; Grunze, M; Nisius, T; Wilhein, T; Stickler, D; Stillrich, H; Frömter, R; Oepen, H-P; Martins, M; Pfau, B; Günther, C M; Könnecke, R; Eisebitt, S; Faatz, B; Guerassimova, N; Honkavaara, K; Kocharyan, V; Treusch, R; Saldin, E; Schreiber, S; Schneidmiller, E A; Yurkov, M V; Weckert, E; Vartanyants, I A

    2009-01-23

    Coherent diffractive imaging for the reconstruction of a two-dimensional (2D) finite crystal structure with a single pulse train of free-electron laser radiation at 7.97 nm wavelength is demonstrated. This measurement shows an advance on traditional coherent imaging techniques by applying it to a periodic structure. It is also significant that this approach paves the way for the imaging of the class of specimens which readily form 2D, but not three-dimensional crystals. We show that the structure is reconstructed to the detected resolution, given an adequate signal-to-noise ratio.

  3. 2-D studies of Relativistic electron beam plasma instabilities in an inhomogeneous plasma

    CERN Document Server

    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...

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

    CERN Document Server

    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.

  5. High Sensitivity 1-D and 2-D Microwave Spectroscopy via Cryogenic Buffer Gas Cooling

    Science.gov (United States)

    Patterson, David; Eibenberger, Sandra

    2017-06-01

    All rotationally resolved spectroscopic methods rely on sources of cold molecules. For the last three decades, the workhorse technique for producing highly supersaturated samples of cold molecules has been the pulsed supersonic jet. We present here progress on our alternative method, cryogenic buffer gas cooling. Our high density, continuous source, and low noise temperature allow us to record microwave spectra at unprecedented sensitivity, with a dynamic range in excess of 10^6 achievable in a few minutes of integration time. This high sensitivity enables new protocols in both 1-D and 2-D microwave spectroscopy, including sensitive chiral analysis via nonlinear three wave mixing and applications as an analytical chemistry tool

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

    Science.gov (United States)

    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

  7. Interactions in 2D electron and hole systems in the intermediate and ballistic regimes

    Energy Technology Data Exchange (ETDEWEB)

    Proskuryakov, Y Y [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Savchenko, A K [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Safonov, S S [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Li, L [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Pepper, M [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Simmons, M Y [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Ritchie, D A [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Linfield, E H [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Kvon, Z D [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation)

    2003-09-05

    In different 2D semiconductor systems we study the interaction correction to the Drude conductivity in the intermediate and ballistic regimes, where the parameter k{sub B}T{tau}/ h-bar changes from 0.1 to 10 ({tau} is momentum relaxation time). The temperature dependence of the resistance and magnetoresistance in parallel and perpendicular magnetic fields is analysed in terms of the recent theories of electron-electron interactions in systems with different degree of disorder and different character of the fluctuation potential. Generally, good agreement is found between the experiments and the theories.

  8. Differential cross sections for single-electron capture in He{sup 2+}-D collisions

    Energy Technology Data Exchange (ETDEWEB)

    Bordenave-Montesquieu, D.; Dagnac, R. [Centre National de la Recherche Scientifique (CNRS), 31 - Toulouse (France)]|[Toulouse-3 Univ., 31 (France)

    1995-06-14

    A translational energy spectroscopy technique was used to study single-electron capture into the He{sup +} (n = 2) and He{sup +} (n 3) states in He{sup 2+}-D collisions. Differential cross sections were determined at 4, 6 and 8 keV in the angular range 5`-1{sup o}30` (laboratory frame). As expected, single-electron capture into the n = 2 state was found to be the dominant process; total cross sections for capture into the He{sup +} (n = 3) state were compared to other experimental and theoretical results. (author).

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. 2D Projection Analysis of GPCR Complexes by Negative Stain Electron Microscopy.

    Science.gov (United States)

    Peisley, Alys; Skiniotis, Georgios

    2015-01-01

    While electron cryo-microscopy (cryo-EM) of biological specimens is the preferred single particle EM method for structure determination, its application is very challenging for the typically small (offer a simple and powerful tool for the rapid evaluation of sample characteristics, such as homogeneity or oligomeric state. When coupled to single particle classification and averaging, negative stain EM can provide valuable information on the overall architecture and dynamics of protein complexes. Here we provide a concise protocol for negative stain imaging and two-dimensional (2D) projection analysis of GPCR complexes, including notes for the intricacies of the application in these biological systems.

  12. Broadband 2D electronic spectroscopy reveals a carotenoid dark state in purple bacteria.

    Science.gov (United States)

    Ostroumov, Evgeny E; Mulvaney, Rachel M; Cogdell, Richard J; Scholes, Gregory D

    2013-04-01

    Although the energy transfer processes in natural light-harvesting systems have been intensively studied for the past 60 years, certain details of the underlying mechanisms remain controversial. We performed broadband two-dimensional (2D) electronic spectroscopy measurements on light-harvesting proteins from purple bacteria and isolated carotenoids in order to characterize in more detail the excited-state manifold of carotenoids, which channel energy to bacteriochlorophyll molecules. The data revealed a well-resolved signal consistent with a previously postulated carotenoid dark state, the presence of which was confirmed by global kinetic analysis. The results point to this state's role in mediating energy flow from carotenoid to bacteriochlorophyll.

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

    Directory of Open Access Journals (Sweden)

    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.

  14. Flexible Transparent Electronic Gas Sensors.

    Science.gov (United States)

    Wang, Ting; Guo, Yunlong; Wan, Pengbo; Zhang, Han; Chen, Xiaodong; Sun, Xiaoming

    2016-07-01

    Flexible and transparent electronic gas sensors capable of real-time, sensitive, and selective analysis at room-temperature, have gained immense popularity in recent years for their potential to be integrated into various smart wearable electronics and display devices. Here, recent advances in flexible transparent sensors constructed from semiconducting oxides, carbon materials, conducting polymers, and their nanocomposites are presented. The sensing material selection, sensor device construction, and sensing mechanism of flexible transparent sensors are discussed in detail. The critical challenges and future development associated with flexible and transparent electronic gas sensors are presented. Smart wearable gas sensors are believed to have great potential in environmental monitoring and noninvasive health monitoring based on disease biomarkers in exhaled gas.

  15. Experimental Route to Scanning Probe Hot Electron Nanoscopy (HENs) Applied to 2D Material

    KAUST Repository

    Giugni, Andrea

    2017-06-09

    This paper presents details on a new experimental apparatus implementing the hot electron nanoscopy (HENs) technique introduced for advanced spectroscopies on structure and chemistry in few molecules and interface problems. A detailed description of the architecture used for the laser excitation of surface plasmons at an atomic force microscope (AFM) tip is provided. The photogenerated current from the tip to the sample is detected during the AFM scan. The technique is applied to innovative semiconductors for applications in electronics: 2D MoS2 single crystal and a p-type SnO layer. Results are supported by complementary scanning Kelvin probe microscopy, traditional conductive AFM, and Raman measurements. New features highlighted by HEN technique reveal details of local complexity in MoS2 and polycrystalline structure of SnO at nanometric scale otherwise undetected. The technique set in this paper is promising for future studies in nanojunctions and innovative multilayered materials, with new insight on interfaces.

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

    CERN Document Server

    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.

  17. Design of the 2D electron cyclotron emission imaging instrument for the J-TEXT tokamak

    Science.gov (United States)

    Pan, X. M.; Yang, Z. J.; Ma, X. D.; Zhu, Y. L.; Luhmann, N. C.; Domier, C. W.; Ruan, B. W.; Zhuang, G.

    2016-11-01

    A new 2D Electron Cyclotron Emission Imaging (ECEI) diagnostic is being developed for the J-TEXT tokamak. It will provide the 2D electron temperature information with high spatial, temporal, and temperature resolution. The new ECEI instrument is being designed to support fundamental physics investigations on J-TEXT including MHD, disruption prediction, and energy transport. The diagnostic contains two dual dipole antenna arrays corresponding to F band (90-140 GHz) and W band (75-110 GHz), respectively, and comprises a total of 256 channels. The system can observe the same magnetic surface at both the high field side and low field side simultaneously. An advanced optical system has been designed which permits the two arrays to focus on a wide continuous region or two radially separate regions with high imaging spatial resolution. It also incorporates excellent field curvature correction with field curvature adjustment lenses. An overview of the diagnostic and the technical progress including the new remote control technique are presented.

  18. Design of the 2D electron cyclotron emission imaging instrument for the J-TEXT tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Pan, X. M.; Yang, Z. J., E-mail: yangzj@hust.edu.cn; Ma, X. D.; Ruan, B. W.; Zhuang, G. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Zhu, Y. L. [School of Physics, University of Science and Technology of China, Anhui 230026 (China); Luhmann, N. C.; Domier, C. W. [Davis Millimeter Wave Research Center, University of California, Davis, California 95616 (United States)

    2016-11-15

    A new 2D Electron Cyclotron Emission Imaging (ECEI) diagnostic is being developed for the J-TEXT tokamak. It will provide the 2D electron temperature information with high spatial, temporal, and temperature resolution. The new ECEI instrument is being designed to support fundamental physics investigations on J-TEXT including MHD, disruption prediction, and energy transport. The diagnostic contains two dual dipole antenna arrays corresponding to F band (90-140 GHz) and W band (75-110 GHz), respectively, and comprises a total of 256 channels. The system can observe the same magnetic surface at both the high field side and low field side simultaneously. An advanced optical system has been designed which permits the two arrays to focus on a wide continuous region or two radially separate regions with high imaging spatial resolution. It also incorporates excellent field curvature correction with field curvature adjustment lenses. An overview of the diagnostic and the technical progress including the new remote control technique are presented.

  19. Electronic and optical properties of strained graphene and other strained 2D materials: a review

    Science.gov (United States)

    Naumis, Gerardo G.; Barraza-Lopez, Salvador; Oliva-Leyva, Maurice; Terrones, Humberto

    2017-09-01

    This review presents the state of the art in strain and ripple-induced effects on the electronic and optical properties of graphene. It starts by providing the crystallographic description of mechanical deformations, as well as the diffraction pattern for different kinds of representative deformation fields. Then, the focus turns to the unique elastic properties of graphene, and to how strain is produced. Thereafter, various theoretical approaches used to study the electronic properties of strained graphene are examined, discussing the advantages of each. These approaches provide a platform to describe exotic properties, such as a fractal spectrum related with quasicrystals, a mixed Dirac–Schrödinger behavior, emergent gravity, topological insulator states, in molecular graphene and other 2D discrete lattices. The physical consequences of strain on the optical properties are reviewed next, with a focus on the Raman spectrum. At the same time, recent advances to tune the optical conductivity of graphene by strain engineering are given, which open new paths in device applications. Finally, a brief review of strain effects in multilayered graphene and other promising 2D materials like silicene and materials based on other group-IV elements, phosphorene, dichalcogenide- and monochalcogenide-monolayers is presented, with a brief discussion of interplays among strain, thermal effects, and illumination in the latter material family.

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

    Science.gov (United States)

    Pronschinske, Alex; Pedevilla, Philipp; Murphy, Colin J.; Lewis, Emily A.; Lucci, Felicia R.; Brown, Garth; Pappas, George; Michaelides, Angelos; Sykes, E. Charles H.

    2015-09-01

    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. Here, we synthesize one-atom-thick films of the radioactive isotope 125I on gold that are stable under ambient conditions. Scanning tunnelling microscopy, supported by electronic structure simulations, allows us to directly observe nuclear transmutation of individual 125I atoms into 125Te, and explain the surprising stability of the 2D film as it underwent radioactive decay. The metal interface geometry induces a 600% amplification of low-energy electron emission (<10 eV; ref. ) compared with atomic 125I. This enhancement of biologically active low-energy electrons might offer a new direction for highly targeted nanoparticle therapies.

  1. The success of Fermi gas model for overall scaling of 2D metal-to-insulator transition data

    Science.gov (United States)

    Cheremisin, M. V.

    2017-03-01

    The melting condition for two-dimensional Wigner solid (Platzman and Fukuyama, 1974) [14] is shown to contain an error of a factor of π. The analysis of experimental data for apparent 2D metal-to-insulator transition shows that the Wigner solidification (Tanatar and Ceperley, 1989) [16] has been never achieved. Within routine Fermi gas model both the metallic and insulating behavior of different 2D system for actual range of carrier densities and temperatures is explained.

  2. Intracellular ROS mediates gas plasma-facilitated cellular transfection in 2D and 3D cultures

    Science.gov (United States)

    Xu, Dehui; Wang, Biqing; Xu, Yujing; Chen, Zeyu; Cui, Qinjie; Yang, Yanjie; Chen, Hailan; Kong, Michael G.

    2016-01-01

    This study reports the potential of cold atmospheric plasma (CAP) as a versatile tool for delivering oligonucleotides into mammalian cells. Compared to lipofection and electroporation methods, plasma transfection showed a better uptake efficiency and less cell death in the transfection of oligonucleotides. We demonstrated that the level of extracellular aqueous reactive oxygen species (ROS) produced by gas plasma is correlated with the uptake efficiency and that this is achieved through an increase of intracellular ROS levels and the resulting increase in cell membrane permeability. This finding was supported by the use of ROS scavengers, which reduced CAP-based uptake efficiency. In addition, we found that cold atmospheric plasma could transfer oligonucleotides such as siRNA and miRNA into cells even in 3D cultures, thus suggesting the potential for unique applications of CAP beyond those provided by standard transfection techniques. Together, our results suggest that cold plasma might provide an efficient technique for the delivery of siRNA and miRNA in 2D and 3D culture models. PMID:27296089

  3. Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments

    Energy Technology Data Exchange (ETDEWEB)

    Krishna, R.; Baten, J.M. van

    1999-10-01

    About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions. The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.

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

    Directory of Open Access Journals (Sweden)

    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. The ionized gas in the central region of NGC 5253. 2D mapping of the physical and chemical properties

    Science.gov (United States)

    Monreal-Ibero, A.; Walsh, J. R.; Vílchez, J. M.

    2012-08-01

    Context. Blue compact dwarf (BCD) galaxies constitute the ideal laboratories to test the interplay between massive star formation and the surrounding gas. As one of the nearest BCD galaxies, NGC 5253 was previously studied with the aim to elucidate in detail the starburst interaction processes. Some open issues regarding the properties of its ionized gas still remain to be addressed. Aims: The 2D structure of the main physical and chemical properties of the ionized gas in the core of NGC 5253 has been studied. Methods: Optical integral field spectroscopy (IFS) data has been obtained with FLAMES Argus and lower resolution gratings of the Giraffe spectrograph. Results: We derived 2D maps for different tracers of electron density (ne), electron temperature (Te) and ionization degree. The maps for ne as traced by [O ii], [S ii], [Fe iii], and [Ar iv] line ratios are compatible with a 3D stratified view of the nebula with the highest ne in the innermost layers and a decrease of ne outwards. 2D maps of Te were measured from [O iii] and [S ii] line ratios; to our knowledge, this is the first time that a Te map based on [S ii] lines for an extragalactic object has been presented. The joint interpretation of the Te([S ii]) and Te([O iii]) maps is consistent with a Te structure in 3D with higher temperatures close to the main ionizing source surrounded by a colder and more diffuse component. The highest ionization degree is found at the peak of emission for the gas with relatively high ionization in the main Giant H ii Region and lower ionization degree delineating the more extended diffuse component. We derived abundances of oxygen, neon, argon, and nitrogen. Abundances for O, Ne and Ar are constant over the mapped area within ≲0.1 dex. The mean 12 + log (O/H) is 8.26 ± 0.04 while the relative abundances of log (N/O), log (Ne/O) and log (Ar/O) were ~-1.32 ± 0.05, -0.65 ± 0.03 and -2.33 ± 0.06, respectively. There are two locations with enhanced N/O. The first (log (N

  6. 2D positive streamer modelling in NTP air under extreme pulse fronts. What about runaway electrons?

    Science.gov (United States)

    Marode, E.; Dessante, Ph; Tardiveau, P.

    2016-12-01

    Using a 2D model, an attempt is made to understand the properties and aspects of a diffuse discharge, appearing in a positive point-to-plane gap submitted to very high voltage pulses. After presenting the model, comparisons between the computed low and high pulse heights of 10 kV and 50 kV, respectively, will be shown and analysed. A streamer ionising wave is still formed, but its role in ionising a region of low field is replaced by the role of providing a plasma within which the electrons will benefit from the presence of a high electrical field meant to induce strong electron collision activities. A comparison between the aspect of the computed and experimental discharge carried out in the same conditions at 50 kV will be presented, which seems to be in agreement with the diffuse aspect. Although the difference in order of magnitude of the speed of development and the height of the current must be underlined, similarities between the structures of both situations will, however, be recognised. A high probability of obtaining highly energetic electrons and runaways (RAEs) will also be derived following a simple approach.

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

    Energy Technology Data Exchange (ETDEWEB)

    Szoecs, V., E-mail: szocs@fns.uniba.sk [Institute of Chemistry, Comenius University, Mlynska dolina CH2, 842 15 Bratislava (Slovakia)

    2011-05-26

    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: {yields} RWA approach to electronic photon echo. {yields} A straightforward calculation of 2D electronic spectrograms in finite molecular systems. {yields} 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 {delta}-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.

  8. STUDY OF AXIAL VELOCITY IN GAS CYCLONES BY 2D-PIV, 3D-PIY, AND SIMULATION

    Institute of Scientific and Technical Information of China (English)

    Zhengliang Liu; Jinyu Jiao; Ying Zheng

    2006-01-01

    The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry (2D-PIV) and three-dimensional particle image velocimetry (3D-PIV) experiments in this study. Due to the limitation of 2D-PIV configuration, the contamination generated by the strong tangential velocity in the cyclone can be registered in the axial velocity detected by 2D-PIV. Efficient methods are proposed in this work to remove this contamination. The contamination-removed 2D-PIV data agree well with 3D-PIV results. The distributions of the axial velocity are also computed by the Reynolds stress model (RSM) and verified using the PIV experimental results. Reasonable agreements are obtained.

  9. c2d Spitzer IRS spectra of embedded low-mass young stars : gas-phase emission lines

    NARCIS (Netherlands)

    Lahuis, F.; van Dishoeck, E. F.; Jorgensen, J. K.; Blake, G. A.; Evans, N. J.

    2010-01-01

    Context. A survey of mid-infrared gas-phase emission lines of H(2), H(2)O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer "Cores to Disks" (c2d) legacy program. Aims. The environment of embed

  10. Tunable electron heating induced giant magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system

    Science.gov (United States)

    Wang, Zhuo; Samaraweera, R. L.; Reichl, C.; Wegscheider, W.; Mani, R. G.

    2016-12-01

    Electron-heating induced by a tunable, supplementary dc-current (Idc) helps to vary the observed magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system. The magnetoresistance at B = 0.3 T is shown to progressively change from positive to negative with increasing Idc, yielding negative giant-magnetoresistance at the lowest temperature and highest Idc. A two-term Drude model successfully fits the data at all Idc and T. The results indicate that carrier heating modifies a conductivity correction σ1, which undergoes sign reversal from positive to negative with increasing Idc, and this is responsible for the observed crossover from positive- to negative- magnetoresistance, respectively, at the highest B.

  11. Upgrade of PARC2D to include real gas effects. [computer program for flowfield surrounding aeroassist flight experiment

    Science.gov (United States)

    Saladino, Anthony; Praharaj, Sarat C.; Collins, Frank G.; Seaford, C. Mark

    1990-01-01

    This paper presents a description of the changes and additions to the perfect gas PARC2D code to include chemical equilibrium effects, resulting in a code called PARCEQ2D. The work developed out of a need to have the capability of more accurately representing the flowfield surrounding the aeroassist flight experiment (AFE) vehicle. Use is made of the partition function of statistical mechanics in the evaluation of the thermochemical properties. This approach will allow the PARC code to be extended to thermal nonequilibrium when this task is undertaken in the future. The transport properties follow from formulae from the kinetic theory of gases. Results are presented for a two-dimensional AFE that compare perfect gas and real gas solutions at flight conditions, showing vast differences between the two cases.

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

    CERN Document Server

    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...

  13. Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

    KAUST Repository

    Anasori, Babak

    2016-02-24

    In this study, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M3C2 and M4C3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX]nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M′2M′′C2 and M′2M′′2C3 – where M′ and M′′ are two different early transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M′ atoms only occupy the outer layers and the M′′ atoms fill the middle layers. In other words, M′ atomic layers sandwich the middle M′′–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo2TiC2 and Mo2Ti2C3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC]nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti3C2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo2TiC2Tx exhibits semiconductor-like transport behavior, while Ti3C2Tx is a metal. This finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.

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

    CERN Document Server

    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...

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

    CERN Document Server

    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...

  16. Effective masses of Quasi-2D electrons in InGaAs/GaAsSb modulation-doped heterostructures

    Science.gov (United States)

    Tanveer, Imtiaz; McCombe, Bruce; Detz, Hermann; Strasser, Gottfried

    2015-03-01

    The electronic properties of In0.53Ga0.47As/GaAs0.51Sb0.49 2D electron gas (2DEG) systems, in spite of their use in high power electronics, have not been extensively investigated. Recently, they have been suggested as potential materials for IR quantum devices such as quantum cascade lasers (QCL), and they also show a strong Rashba effect1,2. Here accurate values of the effective masses are important. Two remotely donor (Si)-doped samples grown by MBE with a 2DEG at the single heterostructure interface were studied by FIR magneto-transmission spectroscopy with a BOMEM FTIR spectrometer. The maximum mobilities (near 70 K) are 43,000 cm2/Vs and 36,000 cm2/Vs with corresponding carrier densities of 1.07 x 1012 cm-2 and 2.13 x 1012 cm-2, respectively. Cyclotron resonance measurements between 4T and 9T yielded m* = 0.0495m0 for the more heavily doped sample. Individual transmission profiles in this case showed broadening toward high-energy, which may be due to contributions to the overall absorption profile from higher occupied subbands. The lower density sample shows an energy vs B dependence that does not extrapolate to zero at B = 0. The origin of this behavior will be discussed. Work at UB supported in part by NSF DMR #1305770 and the Office of the Provost and at the TU Wien by the Austrian Science Fund (FWF): P26100-N27 (H2N) and F4909-N23 (NextLite).

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

    Science.gov (United States)

    Sengupta, M.; Ganesh, R.

    2016-10-01

    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. A cross section of the trapped non neutral cloud composed of electrons mixed uniformly with a fractional population of ions is loaded on a 2D PIC grid with the plasma in a state of unstable equilibrium due to differential rotation between the electron and the ion component. The electrons are also loaded with an axial velocity component, vz, that mimics their bouncing motion between the electrostatic end plugs of a Penning-Malmberg trap. This vz loading facilitates 3D elastic and excitation collisions of the electrons with background neutrals under a MCC scheme. In the present set of numerical experiments, the electrons do not ionize the neutrals. This helps in separating out only the effect of non-ionizing collisions of electrons on the dynamics of the cloud. Simulations reveal that these non-ionizing collisions indirectly influence the ensuing collisionless ion resonance instability of the contaminated electron cloud by a feedback process. The collisional relaxation reduces the average density of the electron cloud and thereby increases the fractional density of the ions mixed in it. The dynamically changing electron density and fractional density of ions feed back on the ongoing ion-resonance (two-stream) instability between the two components of the nonneutral cloud and produce deviations in the paths of progression of the instability that are uncorrelated at different background gas pressures. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the 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

  18. RKKY interaction for the spin-polarized electron gas

    Science.gov (United States)

    Valizadeh, Mohammad M.; Satpathy, Sashi

    2015-11-01

    We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky-Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form ℋ = JS1 ṡS2 + D ṡS1 ×S2 + S1 ṡΓ ↔ṡS2. We find that for the spin-polarized electron gas, a nonzero tensor interaction Γ ↔ is present in addition to the scalar RKKY interaction J, while D is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta kF↑ and kF↓, while the R-3 distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.

  19. Probing 2D Quantum Turbulence in Atomic Superfluid Gas using Bragg Scattering

    CERN Document Server

    Seo, Sang Won; Kim, Joon Hyun; Shin, Yong-il

    2016-01-01

    We demonstrate the use of spatially resolved Bragg spectroscopy for detection of the quantum vortex circulation signs in an atomic Bose-Einstein condensate (BEC). High-velocity atoms near the vortex cores are resonantly scattered from the BEC, and the vortex signs are determined from the scattered atom positions relative to the corresponding vortex cores. Using this method, we investigate decaying 2D quantum turbulence in a highly oblate BEC at temperatures of $\\sim 0.5 T_c$, where $T_c$ is the critical temperature of the trapped sample. Clustering of like-sign vortices is not observed; rather, the measured vortex configurations reveal weak pair correlations between the vortices and antivortices in the turbulent BEC. Our Bragg scattering method enables a direct experimental study of 2D quantum turbulence in BECs.

  20. A 2d model for the effect of gas diffusion on mobility of foam for EOR

    NARCIS (Netherlands)

    Nonnekes, L.E.; Cox, S.J.; Rossen, W.R.

    2012-01-01

    Transport of gas across liquid films between bubbles is cited as one reason why CO2 foams for enhanced oil recovery (EOR) are usually weaker than N2 foams and why steam foams are weaker than foams of steam mixed with N2. We examine here the effect of inter-bubble gas diffusion on flowing bubbles in

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

    Fujihashi, Yuta; Fleming, Graham R; Ishizaki, Akihito

    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.

  3. Identifying Shallow Gas Reservoir Using 2D Seismic data and Seismic Attribute Analysis over Shahbazpur Structure, Bhola, Southern Bangladesh.

    Science.gov (United States)

    Rahman, M.; Imam, B.; Kabir, S. M. M.; Mustaque, S.; Gazi, M. Y.

    2016-12-01

    The Shahbazpur structure is a subsurface anticlinal structure situated in the middle of the Bhola Island in the northern margin of Hatia trough of Bengal Foredeep. Bangladesh petroleum exploration and production company Ltd. (BAPEX) discovered the Shahbazpur gas field in its exploration well Shahbazpur-1, in which commercial gas pools were tested positively from depth range of 3154m to 3212m below surface. A method is established to delineate the structural mapping precisely by interpreting Eight 2D seismic lines that are acquired over Shahbazpur structure. Moreover direct hydrocarbon indicators (DHI) related attributes are analyzed for further confirmation for presence of hydrocarbon in shallow to moderate depth. To do this synthetic seismogram generation, seismic to well tie, velocity modelling and depth conversion are performed. A limited number of seismic attributes functions that are available in an academic version of Petrel software are applied to analyze attributes. Seismic attribute analyses that are used in this interpretation mainly are associated to bright spot detection. Seismic indication of gas accumulation in 2D seismic line; RMS amplitude and Envelope attribute map from seismic attribute analysis shows presence of bright spots or high amplitude anomaly above the present Shahbazpur structure reservoir zone. This signature will play a very important role in next well planning on the same structure to test the shallow accumulation of hydrocarbon. For better understanding of this shallow reserve, it is suggested to acquire 3D seismic data over Shahbazpur structure which will help to evaluate the hydrocarbon accumulation and to identify gas migration pathways.

  4. Effects of in-plane magnetic field on the transport of 2D electron vortices in non-uniform plasmas

    Science.gov (United States)

    Angus, Justin; Richardson, Andrew; Schumer, Joseph; Pulsed Power Team

    2015-11-01

    The formation of electron vortices in current-carrying plasmas is observed in 2D particle-in-cell (PIC) simulations of the plasma-opening switch. In the presence of a background density gradient in Cartesian systems, vortices drift in the direction found by crossing the magnetic field with the background density gradient as a result of the Hall effect. However, most of the 2D simulations where electron vortices are seen and studied only allow for in-plane currents and thus only an out-of-plane magnetic field. Here we present results of numerical simulations of 2D, seeded electron vortices in an inhomogeneous background using the generalized 2D electron-magneto-hydrodynamic model that additionally allows for in-plane components of the magnetic field. By seeding vortices with a varying axial component of the velocity field, so that the vortex becomes a corkscrew, it is found that a pitch angle of around 20 degrees is sufficient to completely prevent the vortex from propagating due to the Hall effect for typical plasma parameters. This work is supported by the NRL Base Program.

  5. Acousto-exciton interaction in a gas of 2D indirect dipolar excitons in the presence of disorder

    Energy Technology Data Exchange (ETDEWEB)

    Kovalev, V. M.; Chaplik, A. V., E-mail: chaplik@isp.nsc.ru [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2016-03-15

    A theory for the linear and quadratic responses of a 2D gas of indirect dipolar excitons to an external surface acoustic wave perturbation in the presence of a static random potential is considered. The theory is constructed both for high temperatures, definitely greater than the exciton gas condensation temperature, and at zero temperature by taking into account the Bose–Einstein condensation effects. The particle Green functions, the density–density correlation function, and the quadratic response function are calculated by the “cross” diagram technique. The results obtained are used to calculate the absorption of Rayleigh surface waves and the acoustic exciton gas drag by a Rayleigh wave. The damping of Bogoliubov excitations in an exciton condensate due to theirs scattering by a random potential has also been determined.

  6. Stable and high-power few cycle supercontinuum for 2D ultrabroadband electronic spectroscopy.

    Science.gov (United States)

    Spokoyny, Boris; Koh, Christine J; Harel, Elad

    2015-03-15

    Broadband supercontinuum (SC) pulses in the few cycle regime are a promising source for spectroscopic and imaging applications. However, SC sources are plagued by poor stability, greatly limiting their utility in phase-resolved nonlinear experiments such as 2D photon echo spectroscopy (2D PES). Here, we generated SC by two-stage filamentation in argon and air starting from 100 fs input pulses, which are sufficiently high-power and stable to record time-resolved 2D PE spectra in a single laser shot. We obtain a total power of 400 μJ/pulse in the visible spectral range of 500-850 nm and, after compression, yield pulses with duration of 6 fs according to transient-grating frequency-resolved optical gating (TG-FROG) measurements. We demonstrate the method on the laser dye, Cresyl Violet, and observe coherent oscillations indicative of nuclear wavepacket dynamics.

  7. The Non-selfsimilar Riemann Problem for 2-D Zero-Pressure Flow in Gas Dynamics

    Institute of Scientific and Technical Information of China (English)

    Wenhua SUN; Wancheng SHENG

    2007-01-01

    The non-selfsimilar Riemann problem for two-dimensional zero-pressure flow in gas dynamics with two constant states separated by a convex curve is considered. By means of the generalized Rankine-Hugoniot relation and the generalized characteristic analysis method, the global solution involving delta shock wave and vacuum is constructed. The explicit solution for a special case is also given.

  8. 2D Time-lapse Resistivity Monitoring of an Organic Produced Gas Plume in a Landfill using ERT.

    Science.gov (United States)

    Amaral, N. D.; Mendonça, C. A.; Doherty, R.

    2014-12-01

    This project has the objective to study a landfill located on the margins of Tietê River, in São Paulo, Brazil, using the electroresistivity tomography method (ERT). Due to huge organic matter concentrations in the São Paulo Basin quaternary sediments, there is subsurface depth related biogas accumulation (CH4 and CO2), induced by anaerobic degradation of the organic matter. 2D resistivity sections were obtained from a test area since March 2012, a total of 7 databases, being the last one dated from October 2013. The studied line has the length of 56m, the electrode interval is of 2m. In addition, there are two boreholes along the line (one with 3 electrodes and the other one with 2) in order to improve data quality and precision. The boreholes also have a multi-level sampling system that indicates the fluid (gas or water) presence in relation to depth. With our results it was possible to map the gas plume position and its area of extension in the sections as it is a positive resistivity anomaly, with the gas level having approximately 5m depth. With the time-lapse analysis (Matlab script) between the obtained 2D resistivity sections from the site, it was possible to map how the biogas volume and position change in the landfill in relation to time. Our preliminary results show a preferential gas pathway through the subsurface studied area. A consistent relation between the gas depth and obtained microbiological data from archea and bacteria population was also observed.

  9. Subsurface Gas Flow and Ice Grain Acceleration within Enceladus and Europa Fissures: 2D DSMC Models

    Science.gov (United States)

    Tucker, O. J.; Combi, M. R.; Tenishev, V.

    2014-12-01

    The ejection of material from geysers is a ubiquitous occurrence on outer solar system bodies. Water vapor plumes have been observed emanating from the southern hemispheres of Enceladus and Europa (Hansen et al. 2011, Roth et al. 2014), and N2plumes carrying ice and ark particles on Triton (Soderblom et al. 2009). The gas and ice grain distributions in the Enceladus plume depend on the subsurface gas properties and the geometry of the fissures e.g., (Schmidt et al. 2008, Ingersoll et al. 2010). Of course the fissures can have complex geometries due to tidal stresses, melting, freezing etc., but directly sampled and inferred gas and grain properties for the plume (source rate, bulk velocity, terminal grain velocity) can be used to provide a basis to constrain characteristic dimensions of vent width and depth. We used a 2-dimensional Direct Simulation Monte Carlo (DSMC) technique to model venting from both axi-symmetric canyons with widths ~2 km and narrow jets with widths ~15-40 m. For all of our vent geometries, considered the water vapor source rates (1027­ - 1028 s-1) and bulk gas velocities (~330 - 670 m/s) obtained at the surface were consistent with inferred values obtained by fits of the data for the plume densities (1026 - 1028 s-1, 250 - 1000 m/s) respectively. However, when using the resulting DSMC gas distribution for the canyon geometries to integrate the trajectories of ice grains we found it insufficient to accelerate submicron ice grains to Enceladus' escape speed. On the other hand, the gas distributions in the jet like vents accelerated grains > 10 μm significantly above Enceladus' escape speed. It has been suggested that micron-sized grains are ejected from the vents with speeds comparable to the Enceladus escape speed. Here we report on these results including comparisons to results obtained from 1D models as well as discuss the implications of our plume model results. We also show preliminary results for similar considerations applied to Europa

  10. Development of a selftriggered high counting rate ASIC for readout of 2D gas microstrip neutron detectors

    CERN Document Server

    Brogna, AS; Dabrowski, W; Fiutowski, T; Gebauer, B; Mindur, B; Schmidt, Ch J; Schulz, Ch; Soltveit, H K; Szczygiel, R; Trunk, U; Wiacek, P

    2007-01-01

    In the frame of the DETNI project a 32-channel ASIC suitable for readout of a novel 2D thermal neutron detector based on a hybrid low-pressure Micro-Strip Gas Chamber with solid 157Gd converter has been developed. Each channel delivers position information, a fast time stamp of 2 ns resolution and the signal amplitude (called energy below). The time stamp is used for correlating the signals from X and Y strips while the amplitude is used for finding the center of gravity of a cluster of strips. The timing and energy information are stored in derandomizing buffers and read out via token ring architecture.

  11. A Complete 2D Stability Analysis of Fast MHD Shocks in an Ideal Gas

    Science.gov (United States)

    Trakhinin, Yuri

    An algorithm of numerical testing of the uniform Lopatinski condition for linearized stability problems for 1-shocks is suggested. The algorithm is used for finding the domains of uniform stability, neutral stability, and instability of planar fast MHD shocks. A complete stability analysis of fast MHD shock waves is first carried out in two space dimensions for the case of an ideal gas. Main results are given for the adiabatic constant γ=5/3 (mono-atomic gas), that is most natural for the MHD model. The cases γ=7/5 (two-atomic gas) and γ>5/3 are briefly discussed. Not only the domains of instability and linear (in the usual sense) stability, but also the domains of uniform stability, for which a corresponding linearized stability problem satisfies the uniform Lopatinski condition, are numerically found for different given angles of inclination of the magnetic field behind the shock to the planar shock front. As is known, uniform linearized stability implies the nonlinear stability, that is local existence of discontinuous shock front solutions of a quasilinear system of hyperbolic conservation laws.

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

    Directory of Open Access Journals (Sweden)

    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.

  13. 2D Sn-doped ZnO ultrathin nanosheet networks for enhanced acetone gas sensing application

    KAUST Repository

    Al-Hadeethi, Yas

    2016-11-10

    In this paper, we report the synthesis, characterizations and gas sensing application of 2D Sn-doped ZnO ultrathin nanosheet networks synthesized by a simple and facile hydrothermal process. The synthesized nanosheets were characterized using several techniques in terms of their morphological, structural, optical and compositional properties. The detailed characterizations confirmed that the nanosheets are pure, grown in high-density, possessing well-crystalline wurtzite hexagonal phase and exhibiting good optical properties. Further, the synthesized nanosheets were used as functional material to develop nanosensor device by coating it on the alumina substrate with suitable electrodes. The fabricated sensor device was tested towards acetone gas which exhibited a maximum sensitivity of 5.556 (Ra/Rg) for 200 ppm of acetone at 320 °C.

  14. 2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures

    Science.gov (United States)

    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

  15. Solving structure in the CP29 light harvesting complex with polarization-phased 2D electronic spectroscopy

    Science.gov (United States)

    Ginsberg, Naomi S.; Davis, Jeffrey A.; Ballottari, Matteo; Cheng, Yuan-Chung; Bassi, Roberto; Fleming, Graham R.

    2011-01-01

    The CP29 light harvesting complex from green plants is a pigment-protein complex believed to collect, conduct, and quench electronic excitation energy in photosynthesis. We have spectroscopically determined the relative angle between electronic transition dipole moments of its chlorophyll excitation energy transfer pairs in their local protein environments without relying on simulations or an X-ray crystal structure. To do so, we measure a basis set of polarized 2D electronic spectra and isolate their absorptive components on account of the tensor relation between the light polarization sequences used to obtain them. This broadly applicable advance further enhances the acuity of polarized 2D electronic spectroscopy and provides a general means to initiate or feed back on the structural modeling of electronically-coupled chromophores in condensed phase systems, tightening the inferred relations between the spatial and electronic landscapes of ultrafast energy flow. We also discuss the pigment composition of CP29 in the context of light harvesting, energy channeling, and photoprotection within photosystem II. PMID:21321222

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

    DEFF Research Database (Denmark)

    Mosca, Alessandra; Roberts, Ashley; Daviðsdóttir, Svava

    2011-01-01

    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...... and high resolution) as compared to TEM in the study of polymer nanocomposites. Both microscopy techniques are powerful tools to study these materials and provide a clear, quantitative measurement of the morphology, size distributions, and dispersion of the clay nanoparticles....

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

    Science.gov (United States)

    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).

  18. ``SAFFMAN-TAYLOR'' Finger in 2d Parallel Viscous: BGK Lattice Gas Simulations

    Science.gov (United States)

    Salin, Dominique; Rakotomalala, Nicole; Watzky, Philippe

    1996-11-01

    We study the displacement of miscible fluids between two parallel plates for different values of the Peclet number Pe and of the viscosity ratio M. The full Navier-Stokes problem is addressed. We use the BGK lattice gas method, which is well suited for miscible fluids and allows to introduce molecular diffusion at the microscopic scale of the lattice. This numerical experiment leads to a symmetric concentration profile about the middle of the gap between the plates. At Pe numbers of the order of 1, mixing involves diffusion and advection in the flow direction. At large Pe, the fluids do not mix and an interface between them can be defined. Moreover, above M ~ 10, the interface becomes a well defined finger, the reduced width of which tends to λ_∞=0.56 at large values of M. Assuming that miscible fluids at high Pe numbers are similar to immiscible fluids at high capillary numbers, we find the analytical shape of the finger, using an extrapolation of the Reinelt-Saffman calculations for a Stokes immiscible flow. Surprisingly, the result is that our finger can be deduced from the celebrated Saffman-Taylor' s one, obtained in a potential flow, by a streching in the flow direction by a numerical factor of 2.125.

  19. 2D Spin-Dependent Diffraction of Electrons From Periodical Chains of Nanomagnets

    Directory of Open Access Journals (Sweden)

    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.

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

    NARCIS (Netherlands)

    Tobias, B. J.; Classen, I.G.J.; Domier, C.W.; Heidbrink, W. W.; N C Luhmann Jr.,; Nazikian, R.; Park, H. K.; Spong, D. A.; VanZeeland, M. A.

    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 o

  1. Increasing the lego of 2D electronics materials: silicene and germanene, graphene's new synthetic cousins

    Science.gov (United States)

    Le Lay, Guy; Salomon, Eric; Angot, Thierry; Eugenia Dávila, Maria

    2015-05-01

    The realization of the first Field Effect Transistors operating at room temperature, based on a single layer silicene channel, open up highly promising perspectives, e.g., typically, for applications in digital electronics. Here, we describe recent results on the growth, characterization and electronic properties of novel synthetic two-dimensional materials beyond graphene, namely silicene and germanene, its silicon and germanium counterparts.

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

    Science.gov (United States)

    Mani, R G; Kriisa, A

    2013-12-11

    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 for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare negative diagonal conductivity/resistivity state in the 2DES under photo-excitation should yield a positive diagonal resistance, with a concomitant sign reversal in the Hall voltage.

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

    DEFF Research Database (Denmark)

    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 present data....

  4. 2D electron momentum distributions for transfer ionization in fast proton Helium collisions

    CERN Document Server

    Schoeffler, M S; Houamer, S; Galstyan, A G; Titze, J N; Schmidt, L Ph H; Jahnke, T; Schmidt-Boecking, H; Doerner, R; Popov, Yu V; Gusev, A A; Cappello, C Dal

    2013-01-01

    The momentum distribution of the electron in the reaction p+He $\\rightarrow$ H + He$^{2+}$ + $e$ is measured for projectile energies $E_p$=300 and 630 keV/u at very small scattering angles of hydrogen. We mainly present two dimensional distributions parallel $(k_{||})$ and perpendicular $(k_{\\perp})$ to the projectile beam. Theoretical calculations were carried out within the Plane Wave First Born Approximation (PWFBA), which includes both electron emission mechanisms, shake-off and sequential capture and ionization. It is shown that electron correlations in the target wave function play the most important role in the explanation of experimentally observed backward emission. Second order effects have to be involved to correctly describe the forward emission of the electron.

  5. Mapping of the photo-induced metastable and hidden phases in 2D electronic materials

    Science.gov (United States)

    Zhou, Faran; Sun, Tianyin; Han, Tzong-Ru; Malliakas, Christos; Duxbury, Phillip; Mahanti, Subhendra; Kanatzidis, Mercouri; Ruan, Chong-Yu; MSU Team; NU Team

    Using the ultrafast electron imaging techniques, we studied the light-induced phase transitions in transition-metal dichalcogenide materials. A succession of different phases was introduced transiently using femtosecond mid-infrared pulses and the local atomic scale charge-density-wave dynamics and morphological evolution of the long-range textured domains were in situ characterized using the ultrashort coherent electron pulses. The various metastable and hidden states emerging under the controlled nonthermal, nonadiabatic driving highlight the interaction-driven nature of these transitions with limited involvement of lattice entropy. The methodology introduced here can be generally applied to survey the complex energy landscape in strongly correlated electron systems, avoiding the difficulty of electrostatic gating or confounding effects due to defects and/or disorder. In particular, the observation of robust non-thermal switching at meso-scales and at ultrafast timescales, provides a platform for designing high-speed low-energy consumption nano-photonics and electronics devices.

  6. Spin-Droplet State of an Interacting 2D Electron System

    OpenAIRE

    Teneh, N.; Kuntsevich, A. Yu.; Pudalov, V. M.; Reznikov, M.

    2012-01-01

    We report thermodynamic magnetization measurements of two-dimensional electrons in several high mobility Si metal-oxide-semiconductor field-effect transistors. We provide evidence for an easily polarizable electron state in a wide density range from insulating to deep into the metallic phase. The temperature and magnetic field dependence of the magnetization is consistent with the formation of large-spin droplets in the insulating phase. These droplets melt in the metallic phase with increasi...

  7. c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines

    CERN Document Server

    Lahuis, Fred; Jørgensen, Jes K; Blake, Geoffrey A; Evans, Neal J

    2010-01-01

    A survey of mid-IR gas-phase emission lines of H2, H2O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer "Cores to Disks" (c2d) legacy program. The environment of embedded protostars is complex both in its physical structure (envelopes, outflows, jets, protostellar disks) and the physical processes (accretion, irradiation by UV and/or X-rays, excitation through slow and fast shocks) which take place. A key point is to spatially resolve the emission in the Spitzer-IRS spectra. An optimal extraction method is used to separate both spatially unresolved (compact, up to a few 100 AU) and spatially resolved (extended, 1000 AU or more) emission from the IRS spectra. The results are compared with the c2d disk sample and literature PDR and shock models to address the physical nature of the sources. Both compact and extended emission features are observed. Warm (Tex few 100 K) H2, observed through the pure rotatio...

  8. Spin-droplet state of an interacting 2D electron system.

    Science.gov (United States)

    Teneh, N; Kuntsevich, A Yu; Pudalov, V M; Reznikov, M

    2012-11-30

    We report thermodynamic magnetization measurements of two-dimensional electrons in several high-mobility Si metal-oxide-semiconductor field-effect transistors. We provide evidence for an easily polarizable electron state in a wide density range from insulating to deep into the metallic phase. The temperature and magnetic field dependence of the magnetization is consistent with the formation of large-spin droplets in the insulating phase. These droplets melt in the metallic phase with increasing density and temperature, though they survive up to large densities.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. Electron spectrometer for gas-phase spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Steady-state properties of driven magnetic reconnection in 2D electron magnetohydrodynamics.

    Science.gov (United States)

    Chacón, L; Simakov, Andrei N; Zocco, A

    2007-12-07

    We formulate a rigorous nonlinear analytical model that describes the dynamics of the diffusion (reconnection) region in driven systems in the context of electron magnetohydrodynamics (EMHD). A steady-state analysis yields allowed geometric configurations and associated reconnection rates. In addition to the well-known open X-point geometry, elongated configurations are found possible. The model predictions have been validated numerically with two-dimensional EMHD nonlinear simulations, and are in excellent agreement with previously published work.

  13. Efficient spin-to-charge conversion in the 2D electron liquid at the LAO/STO interface

    Science.gov (United States)

    Chauleau, J.-Y.; Boselli, M.; Gariglio, S.; Weil, R.; de Loubens, G.; Triscone, J.-M.; Viret, M.

    2016-10-01

    Spin-to-charge conversion using the inverse Rashba-Edelstein effect is measured in the 2D electron liquid existing at the interface between LaAlO3 and SrTiO3. The effect is found to be larger than in the highly Rashba split Bi/Ag interface which we attribute to an amplifying effect due to a long carrier's momentum lifetime. The explanation is supported by temperature measurements and the Rashba field is also shown to be anisotropic in the interface plane.

  14. 2D fluid model analysis for the effect of 3D gas flow on a capacitively coupled plasma deposition reactor

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2016-08-19

    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.

  17. Terahertz Induced Photoconductivity of 2D Electron System in HEMT at Low Magnetic Field

    OpenAIRE

    Chebotarev, Andrey; Chebotareva, Galina

    2004-01-01

    A few results of our study of two-dimensional electron system (2DES) in low magnetic fields in GaAs/GaAlAs heterostructures by cyclotron resonance (CR) and photoconductivity techniques are presented. We have first discovered "CR-vanishing effect"in 2DES as well-defined crevasse on CR line in low magnetic fields, when Hall resistance is not quantized. "CR-vanishing effect" indicates vanishing longitudinal resistance & conductivity in these magnetic fields. Observed "CR-vanishing effect" demons...

  18. Single-electron capture in He[sup 2+]-D[sub 2] collisions

    Energy Technology Data Exchange (ETDEWEB)

    Bordenave-Montesquieu, D.; Dagnac, R. (Toulouse-3 Univ., 31 (France))

    1994-02-14

    Doubly differential cross sections of single-electron capture were measured for He[sup 2+] impinging on a molecular deuterium target. The investigated collision energies are 4, 6 and 8 keV and the scattering angles range from 10' to 2[sup o]30' (laboratory frame). The exothermic capture leading to He[sup +] (1s) + D[sub 2][sup +*] was found to be the most important process at low energies and angles, whereas the endothermic channels leading to dissociative capture become the main processes at high scattering angles, i.e. at small impact parameters. (author).

  19. 2D atomic mapping of oxidation states in transition metal oxides by scanning transmission electron microscopy and electron energy-loss spectroscopy

    OpenAIRE

    Tan, H.; Turner, S.; Yücelen, E.; Verbeeck, J.; Van Tendeloo, G.

    2011-01-01

    Abstract: Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn3O4. The Mn L2,3 energy-loss near-edge structures from Mn2+ and Mn3+ cation sites are similar to those of MnO and Mn2O3 references. Comparison with simulations shows that even ...

  20. Electron radiation damage mechanisms in 2D MoSe2

    Science.gov (United States)

    Lehnert, T.; Lehtinen, O.; Algara-Siller, G.; Kaiser, U.

    2017-01-01

    The contributions of different damage mechanisms in single-layer MoSe2 were studied by investigating different MoSe2/graphene heterostructures by the aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) at 80 keV. The damage cross-sections were determined by direct counting of atoms in the AC-HRTEM images. The contributions of damage mechanisms such as knock-on damage or ionization effects were estimated by comparing the damage rates in different heterostructure configurations, similarly to what has been earlier done with MoS2. The behaviour of MoSe2 was found to be nearly identical to that of MoS2, which is an unexpected result, as the knock-on mechanism should be suppressed in MoSe2 due to the high mass of Se, as compared to S.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. Characterization of saturated MHD instabilities through 2D electron temperature profile reconstruction from 1D ECE measurements

    Science.gov (United States)

    Sertoli, M.; Horváth, L.; Pokol, G. I.; Igochine, V.; Barrera, L.

    2013-05-01

    A new method for the reconstruction of two-dimensional (2D) electron temperature profiles in the presence of saturated magneto-hydro-dynamic (MHD) modes from the one-dimensional (1D) electron cyclotron emission (ECE) diagnostic is presented. The analysis relies on harmonic decomposition of the electron temperature oscillations through short time Fourier transforms and requires rigid poloidal mode rotation as the only assumption. The method is applicable to any magnetic perturbation as long as the poloidal and toroidal mode numbers m and n are known. Its application to the case of a (m, n) = (1, 1) internal kink mode on ASDEX Upgrade is presented and a new way to estimate the mode displacement is explained. For such modes, it is shown that the higher order harmonics usually visible in the ECE spectrogram arise also for the pure m = n = 1 mode and that they cannot be directly associated with m = n > 1 magnetic perturbations. This method opens up new possibilities for electron heat transport studies in the presence of saturated MHD modes and a way to disentangle the impurity density contributions from electron temperature effects in the analysis of the soft x-ray data.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  4. Correlations in the impenetrable electron gas

    OpenAIRE

    Göhmann, F.; Its, A. R.; Korepin, V. E.

    1998-01-01

    We consider non-relativistic electrons in one dimension with infinitely strong repulsive delta function interaction. We calculate the long-time, large-distance asymptotics of field-field correlators in the gas phase. The gas phase at low temperatures is characterized by the ideal gas law. We calculate the exponential decay, the power law corrections and the constant factor of the asymptotics. Our results are valid at any temperature. They simplify at low temperatures, where they are easily re...

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

    Science.gov (United States)

    Plenio, M B; Almeida, J; Huelga, S F

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Electronic Properties of a 1D Intrinsic/p-Doped Heterojunction in a 2D Transition Metal Dichalcogenide Semiconductor

    KAUST Repository

    Song, Zhibo

    2017-07-28

    Two-dimensional (2D) semiconductors offer a convenient platform to study 2D physics, for example, to understand doping in an atomically thin semiconductor. Here, we demonstrate the fabrication and unravel the electronic properties of a lateral doped/intrinsic heterojunction in a single-layer (SL) tungsten diselenide (WSe2), a prototype semiconducting transition metal dichalcogenide (TMD), partially covered with a molecular acceptor layer, on a graphite substrate. With combined experiments and theoretical modeling, we reveal the fundamental acceptor-induced p-doping mechanism for SL-WSe2. At the 1D border between the doped and undoped SL-WSe2 regions, we observe band bending and explain it by Thomas-Fermi screening. Using atomically resolved scanning tunneling microscopy and spectroscopy, the screening length is determined to be in the few nanometer range, and we assess the carrier density of intrinsic SL-WSe2. These findings are of fundamental and technological importance for understanding and employing surface doping, for example, in designing lateral organic TMD heterostructures for future devices.

  8. c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines

    Science.gov (United States)

    Lahuis, F.; van Dishoeck, E. F.; Jørgensen, J. K.; Blake, G. A.; Evans, N. J.

    2010-09-01

    Context. A survey of mid-infrared gas-phase emission lines of H2, H2O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer “Cores to Disks” (c2d) legacy program. Aims: The environment of embedded protostars is complex both in its physical structure (envelopes, outflows, jets, protostellar disks) and the physical processes (accretion, irradiation by UV and/or X-rays, excitation through slow and fast shocks) which take place. The mid-IR spectral range hosts a suite of diagnostic lines which can distinguish them. A key point is to spatially resolve the emission in the Spitzer-IRS spectra to separate extended PDR and shock emission from compact source emission associated with the circumstellar disk and jets. Methods: An optimal extraction method is used to separate both spatially unresolved (compact, up to a few hundred AU) and spatially resolved (extended, thousand AU or more) emission from the IRS spectra. The results are compared with the c2d disk sample and literature PDR and shock models to address the physical nature of the sources. Results: Both compact and extended emission features are observed. Warm (T_ex few hundred K) H2, observed through the pure rotational H2 S(0), S(1) and S(2) lines, and [S i] 25 μm emission is observed primarily in the extended component. [S i] is observed uniquely toward truly embedded sources and not toward disks. On the other hand hot (T_ex ⪆ 700 K) H2, observed primarily through the S(4) line, and [Ne ii] emission is seen mostly in the spatially unresolved component. [Fe ii] and [Si ii] lines are observed in both spatial components. Hot H2O emission is found in the spatially unresolved component of some sources. Conclusions: The observed emission on ≥1000 AU scales is characteristic of PDR emission and likely originates in the outflow cavities in the remnant envelope created by the stellar wind and jets from the embedded

  9. A Stochastic Hill Climbing Approach for Simultaneous 2D Alignment and Clustering of Cryogenic Electron Microscopy Images.

    Science.gov (United States)

    Reboul, Cyril F; Bonnet, Frederic; Elmlund, Dominika; Elmlund, Hans

    2016-06-07

    A critical step in the analysis of novel cryogenic electron microscopy (cryo-EM) single-particle datasets is the identification of homogeneous subsets of images. Methods for solving this problem are important for data quality assessment, ab initio 3D reconstruction, and analysis of population diversity due to the heterogeneous nature of macromolecules. Here we formulate a stochastic algorithm for identification of homogeneous subsets of images. The purpose of the method is to generate improved 2D class averages that can be used to produce a reliable 3D starting model in a rapid and unbiased fashion. We show that our method overcomes inherent limitations of widely used clustering approaches and proceed to test the approach on six publicly available experimental cryo-EM datasets. We conclude that, in each instance, ab initio 3D reconstructions of quality suitable for initialization of high-resolution refinement are produced from the cluster centers.

  10. Collective nature of the insulating phase in a strongly interacting 2D electron system at zero magnetic field

    Science.gov (United States)

    Li, Shiqi; Sarachik, M. P.; Shashkin, A. A.; Kravchenko, S. V.

    2015-03-01

    Recent measurements by our group in the low-disorder 2D electron system in silicon have shown that the thermopower diverges at a finite disorder-independent density, providing clear evidence for a transition to a new phase at low density which may be a precursor phase, or a direct transition to the Wigner solid. In agreement with earlier measurements, we report nonlinear I-V characteristics in the insulating phase with a threshold voltage that yields a characteristic length that is too large to be attributed to delocalization of individual electrons. The observed behavior has been attributed to a percolation transition, or to the presence of an additional conduction channel due to a sliding electron solid (Wigner crystal). Our current measurements seek to provide supporting evidence for the presence of a zero-field Wigner solid by detecting the noise generated by the sliding crystallites. Work at CCNY is provided by NSF Grant DMR-1309008 and BSF Grant 2012210; for S. K. by NSF Grant DMR-1309337 and BSF Grant 2012210; for A. A. S. by RFBR Grant 13-02-00095.

  11. Kondo effect at low electron density and high particle-hole asymmetry in 1D, 2D, and 3D

    Science.gov (United States)

    Žitko, Rok; Horvat, Alen

    2016-09-01

    Using the perturbative scaling equations and the numerical renormalization group, we study the characteristic energy scales in the Kondo impurity problem as a function of the exchange coupling constant J and the conduction-band electron density. We discuss the relation between the energy gain (impurity binding energy) Δ E and the Kondo temperature TK. We find that the two are proportional only for large values of J , whereas in the weak-coupling limit the energy gain is quadratic in J , while the Kondo temperature is exponentially small. The exact relation between the two quantities depends on the detailed form of the density of states of the band. In the limit of low electron density the Kondo screening is affected by the strong particle-hole asymmetry due to the presence of the band-edge van Hove singularities. We consider the cases of one- (1D), two- (2D), and three-dimensional (3D) tight-binding lattices (linear chain, square lattice, cubic lattice) with inverse-square-root, step-function, and square-root onsets of the density of states that are characteristic of the respective dimensionalities. We always find two different regimes depending on whether TK is higher or lower than μ , the chemical potential measured from the bottom of the band. For 2D and 3D, we find a sigmoidal crossover between the large-J and small-J asymptotics in Δ E and a clear separation between Δ E and TK for TKband edge. Furthermore, we find that in 1D the particle-hole asymmetry leads to a large decrease of TK compared to the standard result obtained by approximating the density of states to be constant (flat-band approximation), while in 3D the opposite is the case; this is due to the nontrivial interplay of the exchange and potential scattering renormalization in the presence of particle-hole asymmetry. The 2D square-lattice density of states behaves to a very good approximation as a band with constant density of states.

  12. Performance of a Micro-Strip Gas Chamber for event wise, high rate thermal neutron detection with accurate 2D position determination

    Science.gov (United States)

    Mindur, B.; Alimov, S.; Fiutowski, T.; Schulz, C.; Wilpert, T.

    2014-12-01

    A two-dimensional (2D) position sensitive detector for neutron scattering applications based on low-pressure gas amplification and micro-strip technology was built and tested with an innovative readout electronics and data acquisition system. This detector contains a thin solid neutron converter and was developed for time- and thus wavelength-resolved neutron detection in single-event counting mode, which improves the image contrast in comparison with integrating detectors. The prototype detector of a Micro-Strip Gas Chamber (MSGC) was built with a solid natGd/CsI thermal neutron converter for spatial resolutions of about 100 μm and counting rates up to 107 neutrons/s. For attaining very high spatial resolutions and counting rates via micro-strip readout with centre-of-gravity evaluation of the signal amplitude distributions, a fast, channel-wise, self-triggering ASIC was developed. The front-end chips (MSGCROCs), which are very first signal processing components, are read out into powerful ADC-FPGA boards for on-line data processing and thereafter via Gigabit Ethernet link into the data receiving PC. The workstation PC is controlled by a modular, high performance dedicated software suite. Such a fast and accurate system is crucial for efficient radiography/tomography, diffraction or imaging applications based on high flux thermal neutron beam. In this paper a brief description of the detector concept with its operation principles, readout electronics requirements and design together with the signals processing stages performed in hardware and software are presented. In more detail the neutron test beam conditions and measurement results are reported. The focus of this paper is on the system integration, two dimensional spatial resolution, the time resolution of the readout system and the imaging capabilities of the overall setup. The detection efficiency of the detector prototype is estimated as well.

  13. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

    Science.gov (United States)

    Gruznev, D V; Bondarenko, L V; Tupchaya, A Y; Eremeev, S V; Mihalyuk, A N; Chou, J P; Wei, C M; Zotov, A V; Saranin, A A

    2017-01-25

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e.  ∼0.67 ML Tl and  ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  14. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Eremeev, S. V.; Mihalyuk, A. N.; Chou, J. P.; Wei, C. M.; Zotov, A. V.; Saranin, A. A.

    2017-01-01

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), \\sqrt{3}× \\sqrt{3} -(Tl, Pb) and 3× 3 -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)3× 3 compound contains six Tl atoms and seven Pb atoms per 3× 3 unit cell (i.e.  ˜0.67 ML Tl and  ˜0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} and (Tl, Pb)/Ge(1 1 1)3× 3 compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} , these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  15. A Static and Dynamic Investigation of Quantum Nonlinear Transport in Highly Dense and Mobile 2D Electron Systems

    Science.gov (United States)

    Dietrich, Scott

    Heterostructures made of semiconductor materials may be one of most versatile environments for the study of the physics of electron transport in two dimensions. These systems are highly customizable and demonstrate a wide range of interesting physical phenomena. In response to both microwave radiation and DC excitations, strongly nonlinear transport that gives rise to non-equilibrium electron states has been reported and investigated. We have studied GaAs quantum wells with a high density of high mobility two-dimensional electrons placed in a quantizing magnetic field. This study presents the observation of several nonlinear transport mechanisms produced by the quantum nature of these materials. The quantum scattering rate, 1tau/q, is an important parameter in these systems, defining the width of the quantized energy levels. Traditional methods of extracting 1tau/q involve studying the amplitude of Shubnikov-de Haas oscillations. We analyze the quantum positive magnetoresistance due to the cyclotron motion of electrons in a magnetic field. This method gives 1tau/q and has the additional benefit of providing access to the strength of electron-electron interactions, which is not possible by conventional techniques. The temperature dependence of the quantum scattering rate is found to be proportional to the square of the temperature and is in very good agreement with theory that considers electron-electron interactions in 2D systems. In quantum wells with a small scattering rate - which corresponds to well-defined Landau levels - quantum oscillations of nonlinear resistance that are independent of magnetic field strength have been observed. These oscillations are periodic in applied bias current and are connected to quantum oscillations of resistance at zero bias: either Shubnikov-de Haas oscillations for single subband systems or magnetointersubband oscillations for two subband systems. The bias-induced oscillations can be explained by a spatial variation of electron

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

    Enriquez, Miriam M; Akhtar, Parveen; Zhang, Cheng; Garab, Győző; Lambrev, Petar H; Tan, Howe-Siang

    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 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. 3D Reservoir Modeling of Semutang Gas Field: A lonely Gas field in Chittagong-Tripura Fold Belt, with Integrated Well Log, 2D Seismic Reflectivity and Attributes.

    Science.gov (United States)

    Salehin, Z.; Woobaidullah, A. S. M.; Snigdha, S. S.

    2015-12-01

    Bengal Basin with its prolific gas rich province provides needed energy to Bangladesh. Present energy situation demands more Hydrocarbon explorations. Only 'Semutang' is discovered in the high amplitude structures, where rest of are in the gentle to moderate structures of western part of Chittagong-Tripura Fold Belt. But it has some major thrust faults which have strongly breached the reservoir zone. The major objectives of this research are interpretation of gas horizons and faults, then to perform velocity model, structural and property modeling to obtain reservoir properties. It is needed to properly identify the faults and reservoir heterogeneities. 3D modeling is widely used to reveal the subsurface structure in faulted zone where planning and development drilling is major challenge. Thirteen 2D seismic and six well logs have been used to identify six gas bearing horizons and a network of faults and to map the structure at reservoir level. Variance attributes were used to identify faults. Velocity model is performed for domain conversion. Synthetics were prepared from two wells where sonic and density logs are available. Well to seismic tie at reservoir zone shows good match with Direct Hydrocarbon Indicator on seismic section. Vsh, porosity, water saturation and permeability have been calculated and various cross plots among porosity logs have been shown. Structural modeling is used to make zone and layering accordance with minimum sand thickness. Fault model shows the possible fault network, those liable for several dry wells. Facies model have been constrained with Sequential Indicator Simulation method to show the facies distribution along the depth surfaces. Petrophysical models have been prepared with Sequential Gaussian Simulation to estimate petrophysical parameters away from the existing wells to other parts of the field and to observe heterogeneities in reservoir. Average porosity map for each gas zone were constructed. The outcomes of the research

  19. 2D particle-in-cell simulations of the electron drift instability and associated anomalous electron transport in Hall-effect thrusters

    Science.gov (United States)

    Croes, Vivien; Lafleur, Trevor; Bonaventura, Zdeněk; Bourdon, Anne; Chabert, Pascal

    2017-03-01

    In this work we study the electron drift instability in Hall-effect thrusters (HETs) using a 2D electrostatic particle-in-cell (PIC) simulation. The simulation is configured with a Cartesian coordinate system modeling the radial-azimuthal (r{--}θ ) plane for large radius thrusters. A magnetic field, {{B}}0, is aligned along the Oy axis (r direction), a constant applied electric field, {{E}}0, along the Oz axis (perpendicular to the simulation plane), and the {{E}}0× {{B}}0 direction is along the Ox axis (θ direction). Although electron transport can be well described by electron–neutral collisions for low plasma densities, at high densities (similar to those in typical HETs), a strong instability is observed that enhances the electron cross-field mobility; even in the absence of electron–neutral collisions. The instability generates high frequency (of the order of MHz) and short wavelength (of the order of mm) fluctuations in both the azimuthal electric field and charged particle densities, and propagates in the {{E}}0× {{B}}0 direction with a velocity close to the ion sound speed. The correlation between the electric field and density fluctuations (which leads to an enhanced electron–ion friction force) is investigated and shown to be directly responsible for the increased electron transport. Results are compared with a recent kinetic theory, showing good agreement with the instability properties and electron transport.

  20. Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

    Science.gov (United States)

    Morrison, C.; Casteleiro, C.; Leadley, D. R.; Myronov, M.

    2016-09-01

    The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm2/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m0. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour, analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.

  1. Large-Area Chemical Vapor Deposited MoS2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics

    KAUST Repository

    Dai, Zhenyu

    2017-09-08

    2D semiconductors are poised to revolutionize the future of electronics and photonics, much like transparent oxide conductors and semiconductors have revolutionized the display industry. Herein, these two types of materials are combined to realize fully transparent 2D electronic devices and circuits. Specifically, a large-area chemical vapor deposition process is developed to grow monolayer MoS2 continuous films, which are, for the first time, combined with transparent conducting oxide (TCO) contacts. Transparent conducting aluminum doped zinc oxide contacts are deposited by atomic layer deposition, with composition tuning to achieve optimal conductivity and band-offsets with MoS2. The optimized process gives fully transparent TCO/MoS2 2D electronics with average visible-range transmittance of 85%. The transistors show high mobility (4.2 cm2 V−1 s−1), fast switching speed (0.114 V dec−1), very low threshold voltage (0.69 V), and large switching ratio (4 × 108). To our knowledge, these are the lowest threshold voltage and subthreshold swing values reported for monolayer chemical vapor deposition MoS2 transistors. The transparent inverters show fast switching properties with a gain of 155 at a supply voltage of 10 V. The results demonstrate that transparent conducting oxides can be used as contact materials for 2D semiconductors, which opens new possibilities in 2D electronic and photonic applications.

  2. Use of micro-photoluminescence as a contactless measure of the 2D electron density in a GaAs quantum well

    Science.gov (United States)

    Kamburov, D.; Baldwin, K. W.; West, K. W.; Lyon, S.; Pfeiffer, L. N.; Pinczuk, A.

    2017-06-01

    We compare micro-photoluminescence (μPL) as a measure of the electron density in a clean, two-dimensional (2D) system confined in a GaAs quantum well (QW) to the standard magneto-transport technique. Our study explores the PL shape evolution across a number of molecular beam epitaxy-grown samples with different QW widths and 2D electron densities and notes its correspondence with the density obtained in magneto-transport measurements on these samples. We also measure the 2D density in a top-gated quantum well sample using both PL and transport and find that the two techniques agree to within a few percent over a wide range of gate voltages. We find that the PL measurements are sensitive to gate-induced 2D density changes on the order of 109 electrons/cm2. The spatial resolution of the PL density measurement in our experiments is 40 μm, which is already substantially better than the millimeter-scale resolution now possible in spatial density mapping using magneto-transport. Our results establish that μPL can be used as a reliable high spatial resolution technique for future contactless measurements of density variations in a 2D electron system.

  3. A study of gas electron multiplier

    Institute of Scientific and Technical Information of China (English)

    AN Shao-Hui; LI Cheng; ZHOU Yi; XU Zi-Zong

    2004-01-01

    A new kind of gas detector based on gas electron multiplier (GEM) is studied for X-ray imaging of high luminosity. A single-GEM device is designed to test the property of GEM foil .The effective gain and counting capability of a double-GEM detector are measured by an X-ray tube with Cu target. An initial X-ray imaging experiment is carried out using a triple-GEM detector and the position resolution of less than 0.1mm is achieved. The 3D distribution of electrostatic field of GEM mesh is also presented.

  4. DC-current induced magneto-oscillations in very high-mobility 2D electron gas

    Science.gov (United States)

    Yang, C. L.; Zhang, Chi; Du, R. R.; Pfeiffer, L. N.; West, K. W.

    2007-03-01

    We report on a systematic experimental study of DC-current induced magneto-oscillations [1] using Hall bar samples of very high-mobility (8-20 x 10^6 cm^2/Vs) GaAs/AlxGa1-xAs heterostructures. Previously we show that remarkable nonlinear resistance and 1/B oscillations can arise when a high bias current (Ix) is passed through a Hall bar (width w), and the effect can be explained by a Zener tunneling model in the presence of a tilting Hall field [1]. Data of resistance Rxx≡Vx/Ix, differential resistance rxx≡Vx/Ix, and rxx'≡rxx/Ix in higher mobility samples, which show higher order oscillations, have confirmed the validity of this model. Our temperature dependent date show that this effect can persist to kBT>φc, where φc is the cyclotron energy. [1] Yang et al, Phys. Rev. Lett. 89, 076801 (2002).

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

    Directory of Open Access Journals (Sweden)

    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.

  6. Electronic Desorption of gas from metals

    Energy Technology Data Exchange (ETDEWEB)

    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.

  7. Gas Electron multipliers for low energy beams

    CERN Document Server

    Arnold, F; Ropelewski, L; Spanggaard, J; Tranquille, G

    2010-01-01

    Gas Electron Multipliers (GEM) find their way to more and more applications in beam instrumentation. Gas Electron Multiplication uses a very similar physical phenomenon to that of Multi Wire Proportional Chambers (MWPC) but for small profile monitors they are much more cost efficient both to produce and to maintain. This paper presents the new GEM profile monitors intended to replace the MWPCs currently used at CERN’s low energy Antiproton Decelerator (AD). It will be shown how GEMs overcome the documented problems of profile measurements with MWPCs for low energy beams, where the interaction of the beam with the detector has a large influence on the measured profile. Results will be shown of profile measurements performed at 5 MeV using four different GEM prototypes, with discussion on the possible use of GEMs at even lower energies needed at the AD in 2013.

  8. Antiproton beam profile measurements using Gas Electron Multipliers

    CERN Document Server

    Pinto, Serge Duarte; Spanggaard, Jens; Tranquille, Gerard

    2011-01-01

    The new beam profile measurement for the Antiproton Decelerator (AD) at CERN is based on a single Gas Electron Multiplier (GEM) with a 2D readout structure. This detector is very light, ~0.4% X_0, as required by the low energy of the antiprotons, 5.3 MeV. This overcomes the problems previously encountered with multi-wire proportional chambers (MWPC) for the same purpose, where beam interactions with the detector severely affect the obtained profiles. A prototype was installed and successfully tested in late 2010, with another five detectors now installed in the ASACUSA and AEgIS beam lines. We will provide a detailed description of the detector and discuss the results obtained. The success of these detectors in the AD makes GEM-based detectors likely candidates for upgrade of the beam profile monitors in all experimental areas at CERN. The various types of MWPC currently in use are aging and becoming increasingly difficult to maintain.

  9. Electron beam flue gas treatment process. Review

    Energy Technology Data Exchange (ETDEWEB)

    Honkonen, V.A. [Kuopio Univ. (Finland). Dept. of Physics; Chmielewski, A.G. [Institute of Nuclear Chemistry and Technology, Warsaw (Poland)

    1996-12-31

    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 SO{sub 2} and NO{sub x} 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.

  10. Controlling the electronic and geometric structures of 2D insertions to realize high performance metal/insertion-MoS2 sandwich interfaces.

    Science.gov (United States)

    Su, Jie; Feng, Liping; Zeng, Wei; Liu, Zhengtang

    2017-06-08

    Metal/insertion-MoS2 sandwich interfaces are designed to reduce the Schottky barriers at metal-MoS2 interfaces. The effects of geometric and electronic structures of two-dimensional (2D) insertion materials on the contact properties of metal/insertion-MoS2 interfaces are comparatively studied by first-principles calculations. Regardless of the geometric and electronic structures of 2D insertion materials, Fermi level pinning effects and charge scattering at the metal/insertion-MoS2 interface are weakened due to weak interactions between the insertion and MoS2 layers, no gap states and negligible structural deformations for MoS2 layers. The Schottky barriers at metal/insertion-MoS2 interfaces are induced by three interface dipoles and four potential steps that are determined by the charge transfers and structural deformations of 2D insertion materials. The lower the electron affinities of 2D insertion materials, the more are the electrons lost from the Sc surface, resulting in lower n-type Schottky barriers at Sc/insertion-MoS2 interfaces. The larger the ionization potentials and the thinner the thicknesses of 2D insertion materials, the fewer are the electrons that accumulate at the Pt surface, leading to lower p-type Schottky barriers at Pt/insertion-MoS2 interfaces. All Sc/insertion-MoS2 interfaces exhibited ohmic characters. The Pt/BN-MoS2 interface exhibits the lowest p-type Schottky barrier of 0.52 eV due to the largest ionization potential (∼6.88 eV) and the thinnest thickness (single atomic layer thickness) of BN. These results in this work are beneficial to understand and design high performance metal/insertion-MoS2 interfaces through 2D insertion materials.

  11. Growth of 2D sheets of a MOF on graphene surfaces to yield composites with novel gas adsorption characteristics.

    Science.gov (United States)

    Kumar, Ram; Jayaramulu, Kolleboyina; Maji, Tapas Kumar; Rao, C N R

    2014-05-28

    Homogeneous graphene-MOF composites based on a 2D pillared-bilayer MOF (Cd-PBM), {[Cd4(azpy)2(pyrdc)4(H2O)2]·9H2O}n (azpy = 4,4'-azopyridine, pyrdc = pyridine-2,3-dicarboxylate), have been synthesized, using both graphene oxide (GO) and benzoic acid functionalized graphene (BFG). The composites GO@Cd-PBM and BFG@Cd-PBM demonstrate growth of the 2D nano-sheets of MOF on the graphene surface. While the pristine MOF, Cd-PBM shows selective CO2 uptake with a single-step type-I adsorption profile, the composites show stepwise CO2 uptake with a large hysteresis. With H2O and MeOH, on the other hand, the composites show a single-step adsorption unlike the parent MOF.

  12. Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces

    OpenAIRE

    Nanda, B. R. K.; Satpathy, S.

    2008-01-01

    The formation of a novel spin-polarized 2D electron gas at the LaMnO$_3$ monolayer embedded in SrMnO$_3$ is predicted from the first-principles density-functional calculations. The La (d) electrons become confined in the direction normal to the interface in the potential well of the La layer, serving as a positively-charged layer of electron donors. These electrons mediate a ferromagnetic alignment of the Mn t$_{2g}$ spins near the interface via the Anderson-Hasegawa double exchange and becom...

  13. Effects of stacking order, layer number and external electric field on electronic structures of few-layer C2N-h2D.

    Science.gov (United States)

    Zhang, Ruiqi; Li, Bin; Yang, Jinlong

    2015-09-07

    Recently, a new type of two-dimensional layered material, i.e. a nitrogenated holey two-dimensional structure C2N-h2D, has been synthesized using a simple wet-chemical reaction and used to fabricate a field-effect transistor device (Nat. Commun., 2015, 6, 6486). Here we have performed a first-principles study of the electronic properties of few-layer C2N-h2D with different stacking orders and layer numbers. Because of the interlayer coupling mainly in terms of the orbital interaction, band structure of this system, especially splitting of the bands and band gap, depends on its stacking order between the layers, and the band gap exhibits monotonically decreasing behavior as the layer number increases. All the few-layer C2N-h2D materials have characteristics of direct band gap, irrespective of the stacking order and layer number examined in our calculations. And bulk C2N-h2D has an indirect or direct band gap, depending on the stacking order. Besides, when we apply an out-of-plane electric field on few-layer C2N-h2D, its band gap will decrease as the electric field increases due to a giant Stark effect except for the monolayer case, and even a semiconductor-to-metal transition may occur for few-layer C2N-h2D with more layers under an appropriate electric field. Owing to their tunable band gaps in a wide range, the layered C2N-h2D materials will have tremendous opportunities to be applied in nanoscale electronic and optoelectronic devices.

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

    Science.gov (United States)

    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.

  15. Electronic properties of rare gas molecules

    Science.gov (United States)

    Castex, Marie-Claude

    In the theoretical bases for the electronic structures of excited homonuclear dimers, the molecular excited states are Rydberg in character, and their qualitative behavior can be deduced from that of the dimer ions. The derivation of accurate gas adiabatic potential curves in the full distance range requires calculations accounting not only for repulsive and overlap effects that induce the characteristic excimer well depths, but also for the long-range forces, and especially for dispersion. Attention is given to experimental results furnishing useful tests for the theoretical potential curves in a large domain of internuclear distances.

  16. Comparison between 2D and 3D codes in dynamical simulations of gas flow in barred galaxies

    NARCIS (Netherlands)

    Perez, I.

    2008-01-01

    Context. One of the ways to determine the contribution of the dark halo to the gravitational potential of a galaxy is study non-circular (streaming) motions and the associated gas shocks in the bar region. These motions, determined by the potential in the inner parts, can break the disk-halo degener

  17. Glitter in a 2D monolayer.

    Science.gov (United States)

    Yang, Li-Ming; Dornfeld, Matthew; Frauenheim, Thomas; Ganz, Eric

    2015-10-21

    We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.

  18. Fermi-liquid behaviour of the low-density 2D hole gas in GaAs/AlGaAs heterostructure at large values of r_s

    OpenAIRE

    Proskuryakov, Y. Y.; Savchenko, A. K.; Safonov, S. S.; Pepper, M; Simmons, M.Y.; Ritchie, D. A.

    2001-01-01

    We examine the validity of the Fermi-liquid description of the dilute 2D hole gas in the crossover from 'metallic'-to-'insulating' behaviour of R(T).It has been established that, at r_s as large as 29, negative magnetoresistance does exist and is well described by weak localisation. The dephasing time extracted from the magnetoresistance is dominated by the T^2 -term due to Landau scattering in the clean limit. The effect of hole-hole interactions, however, is suppressed when compared with th...

  19. 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

    Science.gov (United States)

    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.

  20. 2D numerical simulation of gas flow interaction with a solid wall by regularized Grad's set of equations

    Science.gov (United States)

    Timokhin, M. Yu.; Ivanov, I. E.; Kryukov, I. A.

    2012-11-01

    This study is devoted to the two-dimensional numerical simulation of gas flow in the transition regime with solid wall interaction. The regularized 13-moment Grad's set of equations (R13) [1,2] was chosen as a mathematical model. A variant of explicit high order Godunov-type scheme with linear flow parameter reconstruction is used for the numerical solution of this set of equations. Numerical method for wall boundary conditions is based on Newton's iterative method suggested here. Couette and Poiseuille flows and lid-driven cavity flow were solved as test examples with this numerical scheme.

  1. 2D and 3D Eulerian Simulations of the Dynamics and Gas and Aerosol Chemistry of a Young Biomass Burning Smoke Plume from a Savannah Fire

    Science.gov (United States)

    Alvarado, M. J.; Prinn, R. G.

    2007-12-01

    The growth of aerosol particles and production of ozone in young smoke plumes is the result of a complex interaction between the mean flow in the smoke plume, turbulent diffusion, gas-phase oxidation, coagulation, and mass transfer between phases. Models allow us to separate the effects of these processes and predict their impact on the global environment. We present the results of two and three-dimensional Eulerian simulations of the dynamics and chemistry of the smoke plume formed by the Timbavati savannah fire studied during SAFARI 2000 (Hobbs et al., 2003, JGR, doi:10.1029/2002JD002352). The dynamical model is an extension of an Eulerian cloud-resolving model that has previously been used to study the role of deep convective clouds on tropospheric chemistry (Wang and Prinn, 2000, JGR, 105(D17) 22,269-22,297). The model includes a source of sensible heat, gases, and particles at the surface to simulate the savannah fire. The new gas and aerosol chemistry model includes heterogeneous chemistry, kinetic mass transfer, coagulation and the formation of secondary organic and inorganic aerosol. Photolysis rates are calculated based on the solution of the radiative transfer equation within the plume, including the scattering and absorption of radiation by the smoke aerosols. Our preliminary 2D Eulerian results using standard chemistry and UV fluxes show that the model can simulate the lower but not the higher levels of O3 observed. Also, the simulated 2D O3 field shows a wave-like pattern in the downwind direction, even though the emissions from the fire are held constant. This suggests that plume heterogeneity in the downwind direction may account for some of the observed variability in O3. We will present results of runs incorporating higher resolution calculation of photolysis rates, heterogeneous HONO formation, and gas phase reactions involving the uncharacterized organic compounds observed in the gas phase of the Timbavati plume in order to better simulate these

  2. Tomographic LP-DOAS measurements of 2D trace gas distributions above the city of Heidelberg, Germany

    Energy Technology Data Exchange (ETDEWEB)

    Poehler, Denis; Hartl, Andreas; Platt, Ulrich [Institute of Environmental Physics, University of Heidelberg (Germany)

    2007-07-01

    LP-DOAS (Long Path-Differential Optical Absorption Spectroscopy) is a well known remote sensing technique for measuring the average concentration of tropospheric trace gases along extended light paths in the open atmosphere. In order to retrieve information of the spatial trace gas distribution tomographic LP-DOAS measurements are useful. They combine the measurement along several intersecting light paths with tomographic inversion techniques and allow 2 and 3 dimensional retrieval of trace gas distributions. In a campaign in Heidelberg, Germany, a measurement set-up encompassing a total of 18 horizontal light paths by using three, Multibeam, LP-DOAS instruments is being tested. In the wavelength range from 285 nm to 365 nm the average concentrations of the trace gases NO{sub 2}, SO{sub 2}, O{sub 3}, HCHO and HONO along each light path could be retrieved with a temporal resolution below 15 minutes. The first evaluated data from winter 2005/06 show high accuracy for NO{sub 2} and SO{sub 2} mean concentrations. They allow deriving for these trace gases twodimensional distributions above the city. Different emission sources varying strongly in space and time can be identified. The results demonstrate that tomographic DOAS measurements can be used to study emissions and transport of trace gases and can be used to evaluate models predicting the air quality.

  3. Heat diffusion in the disordered electron gas

    Science.gov (United States)

    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.

  4. An Excel(®)-based visualization tool of 2-D soil gas concentration profiles in petroleum vapor intrusion.

    Science.gov (United States)

    Verginelli, Iason; Yao, Yijun; Suuberg, Eric M

    2016-01-01

    In this study we present a petroleum vapor intrusion tool implemented in Microsoft(®) Excel(®) using Visual Basic for Applications (VBA) and integrated within a graphical interface. The latter helps users easily visualize two-dimensional soil gas concentration profiles and indoor concentrations as a function of site-specific conditions such as source strength and depth, biodegradation reaction rate constant, soil characteristics and building features. This tool is based on a two-dimensional explicit analytical model that combines steady-state diffusion-dominated vapor transport in a homogeneous soil with a piecewise first-order aerobic biodegradation model, in which rate is limited by oxygen availability. As recommended in the recently released United States Environmental Protection Agency's final Petroleum Vapor Intrusion guidance, a sensitivity analysis and a simplified Monte Carlo uncertainty analysis are also included in the spreadsheet.

  5. Insights into the growth rate of spatially evolving plane turbulent free-shear layers from 2D vortex-gas simulations

    Science.gov (United States)

    Suryanarayanan, Saikishan; Narasimha, Roddam

    2017-02-01

    Although the free-shear or mixing layer has been a subject of extensive research over nearly a century, there are certain fundamental issues that remain controversial. These include the influence of initial and downstream conditions on the flow, the effect of velocity ratio across the layer, and the nature of any possible coupling between small scale dynamics and the large scale evolution of layer thickness. In the spirit of the temporal vortex-gas simulations of Suryanarayanan et al. ["Free turbulent shear layer in a point vortex gas as a problem in nonequilibrium statistical mechanics," Phys. Rev. E 89, 013009 (2014)], we revisit the simple 2D inviscid vortex-gas model with extensive computations and detailed analysis, in order to gain insights into some of the above issues. Simulations of the spatially evolving vortex-gas shear layer are carried out at different velocity ratios using a computational model based on the work of Basu et al. ["Vortex sheet simulation of a plane canonical mixing layer," Comput. Fluids 21, 1-30 (1992) and "Modelling plane mixing layers using vortex points and sheets," Appl. Math. Modell. 19, 66-75 (1995)], but with a crucial improvement that ensures conservation of global circulation. The simulations show that the conditions imposed at the origin of the free shear layer and at the exit to the computational domain can affect flow evolution in their respective downstream and upstream neighbourhoods, the latter being particularly strong in the single stream limit. In between these neighbourhoods at the ends is a regime of universal self-preserving growth rate given by a universal function of velocity ratio. The computed growth rates are generally located within the scatter of experimental data on plane mixing layers and closely agree with recent high Reynolds number experiments and 3D large eddy simulation studies. These findings support the view that observed free-shear layer growth can be largely explained by the 2D vortex dynamics of

  6. 2D Particle-In-Cell simulations of the electron-cyclotron instability and associated anomalous transport in Hall-Effect Thrusters

    Science.gov (United States)

    Croes, Vivien; Lafleur, Trevor; Bonaventura, Zdenek; Péchereau, François; Bourdon, Anne; Chabert, Pascal

    2016-09-01

    This work studies the electron-cyclotron instability in Hall-Effect Thrusters (HETs) using a 2D Particle-In-Cell (PIC) simulation. The simulation is configured with a Cartesian coordinate system where a magnetic field, B0, is aligned along the X-axis (radial direction, including absorbing walls), a constant electric field, E0, along the Z-axis (axial direction, perpendicular to simulation plane), and the E0xB0 direction along the Y-axis (O direction, with periodic boundaries). Although for low plasma densities classical electron-neutral collisions theory describes well electron transport, at sufficiently high densities (as measured in HETs) a strong instability can be observed that enhances the electron mobility, even in the absence of collisions. The instability generates high frequency ( MHz) and short wavelength ( mm) fluctuations in both the electric field and charged particle densities. We investigate the correlation between these fluctuations and their role with anomalous electron transport; complementing previous 1D simulations. Plasma is self-consistently heated by the instability, but since the latter does not reach saturation in an infinitely long 2D system, saturation is achieved through implementation of a finite axial length that models convection in E0 direction. With support of Safran Aircraft Engines.

  7. Broadband 2D electronic spectrometer using white light and pulse shaping: noise and signal evaluation at 1 and 100 kHz.

    Science.gov (United States)

    Kearns, Nicholas M; Mehlenbacher, Randy D; Jones, Andrew C; Zanni, Martin T

    2017-04-03

    We have developed a broad bandwidth two-dimensional electronic spectrometer that operates shot-to-shot at repetition rates up to 100 kHz using an acousto-optic pulse shaper. It is called a two-dimensional white-light (2D-WL) spectrometer because the input is white-light supercontinuum. Methods for 100 kHz data collection are studied to understand how laser noise is incorporated into 2D spectra during measurement. At 100 kHz, shot-to-shot scanning of the delays and phases of the pulses in the pulse sequence produces a 2D spectrum 13-times faster and with the same signal-to-noise as using mechanical stages and a chopper. Comparing 100 to 1 kHz repetition rates, data acquisition time is decreased by a factor of 200, which is beyond the improvement expected by the repetition rates alone due to reduction in 1/f noise. These improvements arise because shot-to-shot readout and modulation of the pulse train at 100 kHz enables the electronic coherences to be measured faster than the decay in correlation between laser intensities. Using white light supercontinuum for the pump and probe pulses produces high signal-to-noise spectra on samples with optical densities 200 nm bandwidth.

  8. Determination of the in-plane effective mass and quantum lifetime of 2D electrons in AlGaN/GaN based HEMTs

    Energy Technology Data Exchange (ETDEWEB)

    Celik, Ozlem; Tiras, Engin; Ardali, Sukru [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, 26470 Eskisehir (Turkey); Lisesivdin, Sefer Bora [Department of Physics, Faculty of Science and Arts, Gazi University, Teknikokullar, 06500 Ankara (Turkey); Ozbay, Ekmel [Nanotechnology Research Center, Department of Physics, and Department of Electrical and Electronics Engineering, Bilkent University, Ankara (Turkey)

    2011-05-15

    Magnetoresistance and Hall resistance measurements have been used to investigate the electronic transport properties of AlGaN/GaN based HEMTs. The Shubnikov-de Haas (SdH) oscillations from magnetoresistance, is obtained by fitting the nonoscillatory component to a polynomial of second degree, and then subtracting it from the raw experimental data. It is shown that only first subband is occupied with electrons. The two-dimensional (2D) carrier density and the Fermi energy with respect to subband energy (E{sub F}-E{sub 1}) have been determined from the periods of the SdH oscillations. The in-plane effective mass (m*) and the quantum lifetime ({tau}{sub q}) of electrons have been obtained from the temperature and magnetic field dependencies of the SdH amplitude, respectively. The in-plane effective mass of 2D electrons is in the range between 0.19 m{sub 0} and 0.22 m{sub 0}. Our results for in-plane effective mass are in good agreement with those reported in the literature (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    CERN Document Server

    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...

  10. Terahertz-Induced Magnetoresistance Oscillations in High-Mobility 2D Electron Systems Under Bichromatic and Multichromatic Excitation

    Science.gov (United States)

    Iñarrea, Jesus

    2017-01-01

    In this work, we investigated the magnetotransport under terahertz radiation in high-mobility two-dimensional electron systems, focusing on irradiation by bichromatic and multichromatic terahertz sources. We observed strong modulation of the Shubnikov-de Haas oscillations at sufficient terahertz radiation power. We determined that the origin of the modulation was the interference between the average distance advanced by the scattered electrons between irradiated Landau states and the available initial density of states at a certain magnetic field. In the case of multifrequency illumination, we found that with the appropriate frequencies, the irradiated magnetoresistance could reach an almost zero-resistance state regime even at moderate radiation power.

  11. Fast ion induced shearing of 2D Alfvén eigenmodes measured by electron cyclotron emission imaging.

    Science.gov (United States)

    Tobias, B J; Classen, I G J; Domier, C W; Heidbrink, W W; Luhmann, N C; Nazikian, R; Park, H K; Spong, D A; Van Zeeland, M A

    2011-02-18

    Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfvén 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.

  12. Titanium trisulfide (TiS3): a 2D semiconductor with quasi-1D optical and electronic properties

    Science.gov (United States)

    Island, Joshua O.; Biele, Robert; Barawi, Mariam; Clamagirand, José M.; Ares, José R.; Sánchez, Carlos; van der Zant, Herre S. J.; Ferrer, Isabel J.; D'Agosta, Roberto; Castellanos-Gomez, Andres

    2016-03-01

    We present characterizations of few-layer titanium trisulfide (TiS3) flakes which, due to their reduced in-plane structural symmetry, display strong anisotropy in their electrical and optical properties. Exfoliated few-layer flakes show marked anisotropy of their in-plane mobilities reaching ratios as high as 7.6 at low temperatures. Based on the preferential growth axis of TiS3 nanoribbons, we develop a simple method to identify the in-plane crystalline axes of exfoliated few-layer flakes through angle resolved polarization Raman spectroscopy. Optical transmission measurements show that TiS3 flakes display strong linear dichroism with a magnitude (transmission ratios up to 30) much greater than that observed for other anisotropic two-dimensional (2D) materials. Finally, we calculate the absorption and transmittance spectra of TiS3 in the random-phase-approximation (RPA) and find that the calculations are in qualitative agreement with the observed experimental optical transmittance.

  13. Direct Printing of 1-D and 2-D Electronically Conductive Structures by Molten Lead-Free Solder

    Directory of Open Access Journals (Sweden)

    Chien-Hsun Wang

    2016-12-01

    Full Text Available This study aims to determine the effects of appropriate experimental parameters on the thermophysical properties of molten micro droplets, Sn-3Ag-0.5Cu solder balls with an average droplet diameter of 50 μm were prepared. The inkjet printing parameters of the molten micro droplets, such as the dot spacing, stage velocity and sample temperature, were optimized in the 1D and 2D printing of metallic microstructures. The impact and mergence of molten micro droplets were observed with a high-speed digital camera. The line width of each sample was then calculated using a formula over a temperature range of 30 to 70 °C. The results showed that a metallic line with a width of 55 μm can be successfully printed with dot spacing (50 μm and the stage velocity (50 mm∙s−1 at the substrate temperature of 30 °C. The experimental results revealed that the height (from 0.63 to 0.58 and solidification contact angle (from 72° to 56° of the metallic micro droplets decreased as the temperature of the sample increased from 30 to 70 °C. High-speed digital camera (HSDC observations showed that the quality of the 3D micro patterns improved significantly when the droplets were deposited at 70 °C.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Science.gov (United States)

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

    2016-03-14

    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.

  17. 2D 31P solid state NMR spectroscopy, electronic structure and thermochemistry of PbP7

    Science.gov (United States)

    Benndorf, Christopher; Hohmann, Andrea; Schmidt, Peer; Eckert, Hellmut; Johrendt, Dirk; Schäfer, Konrad; Pöttgen, Rainer

    2016-03-01

    Phase pure polycrystalline PbP7 was prepared from the elements via a lead flux. Crystalline pieces with edge-lengths up to 1 mm were obtained. The assignment of the previously published 31P solid state NMR spectrum to the seven distinct crystallographic sites was accomplished by radio-frequency driven dipolar recoupling (RFDR) experiments. As commonly found in other solid polyphosphides there is no obvious correlation between the 31P chemical shift and structural parameters. PbP7 decomposes incongruently under release of phosphorus forming liquid lead as remainder. The thermal decomposition starts at T>550 K with a vapor pressure almost similar to that of red phosphorus. Electronic structure calculations reveal PbP7 as a semiconductor according to the Zintl description and clearly shows the stereo-active Pb-6s2 lone pairs in the electron localization function ELF.

  18. Electronic and magnetic properties of zigzag C2N-h2D nanoribbons: Edge and width effects

    Science.gov (United States)

    Yu, H. L.; Jiang, X. F.; Cai, M. Q.; Feng, J. F.; Chen, X. S.; Yang, X. F.; Liu, Y. S.

    2017-10-01

    Based on first-principles calculations, we have systematically investigated the structural stability, electronic and magnetic properties of zigzag C2N nanoribbons (ZC2NNRs). Different from zigzag graphene nanoribbons (ZGNRs), the ground states of ZC2NNRs present ferromagnetic metal, antiferromagnetic semiconductor and spin semiconductor dependently on the edge configuration and width of nanoribbons. Our results suggest the ZC2NNRs have great potential applications in spintronic, thermoelectric and optoelectronic devices.

  19. Controlling quantum-beating signals in 2D electronic spectra by packing synthetic heterodimers on single-walled carbon nanotubes

    Science.gov (United States)

    Wang, Lili; Griffin, Graham B.; Zhang, Alice; Zhai, Feng; Williams, Nicholas E.; Jordan, Richard F.; Engel, Gregory S.

    2017-03-01

    In multidimensional spectroscopy, dynamics of coherences between excited states report on the interactions between electronic states and their environment. The prolonged coherence lifetimes revealed through beating signals in the spectra of some systems may result from vibronic coupling between nearly degenerate excited states, and recent observations confirm the existence of such coupling in both model systems and photosynthetic complexes. Understanding the origin of beating signals in the spectra of photosynthetic complexes has been given considerable attention; however, strategies to generate them in artificial systems that would allow us to test the hypotheses in detail are still lacking. Here we demonstrate control over the presence of quantum-beating signals by packing structurally flexible synthetic heterodimers on single-walled carbon nanotubes, and thereby restrict the motions of chromophores. Using two-dimensional electronic spectroscopy, we find that both limiting the relative rotation of chromophores and tuning the energy difference between the two electronic transitions in the dimer to match a vibrational mode of the lower-energy monomer are necessary to enhance the observed quantum-beating signals.

  20. Synthesis of solid textures based on a 2D example: application to the synthesis of 3D carbon structures observed by transmission electronic microscopy

    Science.gov (United States)

    Da Costa, Jean-Pierre; Germain, Christian

    2010-01-01

    We propose a novel parametric approach which aims at the synthesis of anisotropic solid textures from the analysis of a single 2D exemplar. This approach is an extension of the pyramidal scheme of Portilla and Simoncelli. It proceeds in three main steps: first, a 2D analysis of the example is performed which produces a set of reference statistics. Then, 3D reference statistics are inferred from the 2D ones thanks to specific anisotropy assumptions. The final step aims at the synthesis itself: the 3D target statistics are imposed on a random 3D block according to a specific multi resolution pyramidal scheme. The approach is applied to the synthesis of solid textures representative of the structure of dense pre-graphitic carbons. The samples are lattice fringe images obtained by high resolution transmission electronic microscopy (HRTEM). HRTEM samples with increasing structural order are used for the experimental evaluation. The produced solid textures exhibit anisotropy properties similar to those observed in the HRTEM samples. Such an approach can easily be extended to any 3D anisotropic structures showing stacks of layers such as wood grain images, seismic data, etc.

  1. Tailoring the Two Dimensional Electron Gas at Polar ABO3/SrTiO3 Interfaces for Oxide Electronics

    Science.gov (United States)

    Li, Changjian; Liu, Zhiqi; Lü, Weiming; Wang, Xiao Renshaw; Annadi, Anil; Huang, Zhen; Zeng, Shengwei; Ariando; Venkatesan, T.

    2015-08-01

    The 2D electron gas at the polar/non-polar oxide interface has become an important platform for several novel oxide electronic devices. In this paper, the transport properties of a wide range of polar perovskite oxide ABO3/SrTiO3 (STO) interfaces, where ABO3 includes LaAlO3, PrAlO3, NdAlO3, NdGaO3 and LaGaO3 in both crystalline and amorphous forms, were investigated. A robust 4 unit cell (uc) critical thickness for metal insulator transition was observed for crystalline polar layer/STO interface while the critical thickness for amorphous ones was strongly dependent on the B site atom and its oxygen affinity. For the crystalline interfaces, a sharp transition to the metallic state (i.e. polarization catastrophe induced 2D electron gas only) occurs at a growth temperature of 515 °C which corresponds to a critical relative crystallinity of ~70 ± 10% of the LaAlO3 overlayer. This temperature is generally lower than the metal silicide formation temperature and thus offers a route to integrate oxide heterojunction based devices on silicon.

  2. Stopping power of an electron gas with anisotropic temperature

    Science.gov (United States)

    Khelemelia, O. V.; Kholodov, R. I.

    2016-04-01

    A general theory of motion of a heavy charged particle in the electron gas with an anisotropic velocity distribution is developed within the quantum-field method. The analytical expressions for the dielectric susceptibility and the stopping power of the electron gas differs in no way from well-known classic formulas in the approximation of large and small velocities. Stopping power of the electron gas with anisotropic temperature in the framework of the quantum-field method is numerically calculated for an arbitrary angle between directions of the motion of the projectile particle and the electron beam. The results of the numerical calculations are compared with the dielectric model approach.

  3. Spin Polarization of 2D Electrons in GaAs Quantum Wells at ν=1/2 from Gallium NMR Measurements

    Science.gov (United States)

    Freytag, N.; Horvatić, M.; Berthier, C.; Lévy, L.-P.; Melinte, S.; Bayot, V.; Shayegan, M.

    2000-03-01

    The spin polarization (\\cal P) of a two-dimensional electron gas (2DEG) in two GaAs/AlGaAs multiple-quantum-well heterostructures was probed by measurements of magnetic hyperfine shifts of gallium nuclei located in the quantum wells. The low temperature (50 mK Shankar(R. Shankar, cond-mat/9911288.).

  4. Coupling of multi-vibrational modes in bacteriochlorophyll a in solution observed with 2D electronic spectroscopy

    Science.gov (United States)

    Yue, Shuai; Wang, Zhuan; Leng, Xuan; Zhu, Rui-Dan; Chen, Hai-Long; Weng, Yu-Xiang

    2017-09-01

    Low vibrational modes in a range of 80-400 cm-1 for bacteriochlorophyll a are excited and observed as beating dynamics in two-dimensional electronic spectra. A coupled multi-vibrational mode displaced oscillator model is proposed to account for the vibronic coherence. We found that these low frequency vibrational modes are coupled. By comparing the fitted lifetime of the vibrational modes appearing in the beating dynamics for bacteriochlorophyll a and a protein-bound bacteriochlorophyll a dimer B820 probed by transient grating method, it is suggested that the protein scaffold provides a protection effect on the vibronic coherence where no excitonic coherence has be excited.

  5. Assessment of a 2D electronic portal imaging devices-based dosimetry algorithm for pretreatment and in-vivo midplane dose verification

    Science.gov (United States)

    Jomehzadeh, Ali; Shokrani, Parvaneh; Mohammadi, Mohammad; Amouheidari, Alireza

    2016-01-01

    Background: The use of electronic portal imaging devices (EPIDs) is a method for the dosimetric verification of radiotherapy plans, both pretreatment and in vivo. The aim of this study is to test a 2D EPID-based dosimetry algorithm for dose verification of some plans inside a homogenous and anthropomorphic phantom and in vivo as well. Materials and Methods: Dose distributions were reconstructed from EPID images using a 2D EPID dosimetry algorithm inside a homogenous slab phantom for a simple 10 × 10 cm2 box technique, 3D conformal (prostate, head-and-neck, and lung), and intensity-modulated radiation therapy (IMRT) prostate plans inside an anthropomorphic (Alderson) phantom and in the patients (one fraction in vivo) for 3D conformal plans (prostate, head-and-neck and lung). Results: The planned and EPID dose difference at the isocenter, on an average, was 1.7% for pretreatment verification and less than 3% for all in vivo plans, except for head-and-neck, which was 3.6%. The mean γ values for a seven-field prostate IMRT plan delivered to the Alderson phantom varied from 0.28 to 0.65. For 3D conformal plans applied for the Alderson phantom, all γ1% values were within the tolerance level for all plans and in both anteroposterior and posteroanterior (AP-PA) beams. Conclusion: The 2D EPID-based dosimetry algorithm provides an accurate method to verify the dose of a simple 10 × 10 cm2 field, in two dimensions, inside a homogenous slab phantom and an IMRT prostate plan, as well as in 3D conformal plans (prostate, head-and-neck, and lung plans) applied using an anthropomorphic phantom and in vivo. However, further investigation to improve the 2D EPID dosimetry algorithm for a head-and-neck case, is necessary. PMID:28028511

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  8. Singlet delta oxygen production in a 2D micro-discharge array in air: effect of gas residence time and discharge power

    Science.gov (United States)

    Nayak, Gaurav; Santos Sousa, João; Bruggeman, Peter J.

    2017-03-01

    The production of singlet delta oxygen (O2(a 1Δg)) is of growing interest for many applications. We report on the measurement of O2(a 1Δg) and ozone (O3) in a room temperature atmospheric pressure discharge in dry air. The plasma source is a 2D array of micro-discharges generated by an alternating current voltage at 20 kHz. The study focuses on the effect of gas flow through the discharge. The maximum investigated flow rate allows reducing the gas residence time in the discharge zone to half the discharge period. Results indicate that the residence time and discharge power have a major effect on the O2(a 1Δg) production. Different O2(a 1Δg) density dependencies on power are observed for different flow rates. Effects of collisional quenching on the as-produced and measured O2(a 1Δg) densities are discussed. The flow rate also allows for control of the O2(a 1Δg) to O3 density ratio in the effluent from 0.7 to conditions of pure O3.

  9. Fabrication of Novel 2D NiO Nanosheet Branched on 1D-ZnO Nanorod Arrays for Gas Sensor Application

    Directory of Open Access Journals (Sweden)

    Le Thuy Hoa

    2014-01-01

    Full Text Available Fabrication of 3D structures composed of 1D n-type ZnO nanorods (NRs and 2D p-type NiO nanosheets (NSs by a low-cost, low-temperature, and large-area scalable hydrothermal process and its use in highly sensitive NO2 gas sensors were studied. The p-n heterojunctions formed by NiO-ZnO interfaces as well as large area two-dimensional NiO NSs themselves increased the adsorption of NO2. Moreover, the charge transfer between NiO and ZnO enhanced the responsivity and sensitivity of NO2 sensing even at a concentration of 1 ppm. The 30-min NiO NS growth on ZnO NRs in the hybrid sensor showed the highest sensitivity due to the formation of optimum p-n heterojunctions between ZnO NRs and NiO NSs for gas adsorption and carrier transport. Low responsivity toward reducing gases was also observed.

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

    CERN Document Server

    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 ...

  11. A Role of Electron Beam Irradiation in the Property Improvement of Random and 2-D Type Jute/PLA Green Composites

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Donghwan; Ji, Sanggyu; Hwang, Junghyu; Lee, Byungchul [Kumoh National Institute of Technology, Gumi (Korea, Republic of)

    2011-07-01

    The purpose of this research is to improve the interfacial adhesion between natural jute fibers and PlA and the mechanical and thermal properties of jute/PLA green composites by means of electron beam irradiation under optimal conditions for the modification of sustainable and naturally calculably natural fibers. In ths present study, randomly aligned jute fiber/PLA and 2-directionally aligned jute fabric/PLA green composites with jute treated with electron beam at different dosages were fabricated by compression molding method and the effect of electron beam treatment on their mechanical, impact and thermal properties and fracture surfaces was extensively investigated. It was clearly concluded that electron beam irradiation to jute fibers and jute fabrics at 10 kGy was surely improved the tensile, flexural, impact, dynamic mechanical properties, thermal expansion, heat deflection temperature and thermal stability of random jute fiber/PLA and 2-D jute fabric/PLA green composites, All the results were consistent with each other, supporting the positive role of electron beam irradiation on the improved properties of their green composites.

  12. The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen

    Science.gov (United States)

    Voiry, Damien; Fullon, Raymond; Yang, Jieun; de Carvalho Castro E Silva, Cecilia; Kappera, Rajesh; Bozkurt, Ibrahim; Kaplan, Daniel; Lagos, Maureen J.; Batson, Philip E.; Gupta, Gautam; Mohite, Aditya D.; Dong, Liang; Er, Dequan; Shenoy, Vivek B.; Asefa, Tewodros; Chhowalla, Manish

    2016-09-01

    The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ~-0.1 V and ~50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.

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

    Indian Academy of Sciences (India)

    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.

  14. Crystal and electronic characterization of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ozkendir, Osman Murat, E-mail: ozkendir@gmail.com

    2016-02-15

    Highlights: • Crystal and electronic structure properties of Nd{sub x}Ti{sub 1−x}BO{sub 2+d} structure were investigated. • New crystal structures for Nd–Ti complexes are determined. • Distortions in the crystal structure were observed as a result of Boron shortage. • Prominent change in electronic properties of the samples with the increasing Nd amount. - Abstract: Neodymium substituted TiBO{sub 3} samples were investigated according to their crystal, electric and electronic properties. Studies were conducted by X-ray absorption fine structure spectroscopy (XAFS) technique for the samples with different substitutions in the preparation processes. To achieve better crystal structure results during the study, XRD pattern results were supported by extended-XAFS (EXAFS) analysis. The electronic structure analysis were studied by X-ray absorption near-edge structure spectroscopy (XANES) measurements at the room temperatures. Due to the substituted Nd atoms, prominent changes in crystal structure, new crystal geometries for Nd-Ti complexes, phase transitions in the crystals structure were detected according to the increasing Nd substitutions in the samples. In the entire stages of the substitutions, Nd atoms were observed as governing the whole phenomena due to their dominant characteristics in Ti geometries. Besides, electrical resistivity decay was determined in the materials with the increasing amount of Nd substitution.

  15. Exchange effects in a quasi-one-dimensional electron gas

    Science.gov (United States)

    Gold, A.; Ghazali, A.

    1990-04-01

    We calculate the electron exchange of a quasi-one-dimensional electron gas in a quantum-well wire of radius R0. A two-subband model is considered and the exchange self-energy for the first and second subband is calculated under the assumption that only the lowest subband is partially filled with electrons. Band-bending effects are also discussed. Results for the total energy per electron including kinetic and exchange energy are presented.

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

    CERN Document Server

    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...

  17. Decoherence in a Landau Quantized Two Dimensional Electron Gas

    Directory of Open Access Journals (Sweden)

    McGill Stephen A.

    2013-03-01

    Full Text Available We have studied the dynamics of a high mobility two-dimensional electron gas as a function of temperature. The presence of satellite reflections in the sample and magnet can be modeled in the time-domain.

  18. Electromagnetic drift modes in an inhomogeneous electron gas

    DEFF Research Database (Denmark)

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

    CERN Document Server

    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...

  20. ZnO Nanorods on a LaAlO 3 -SrTiO 3 Interface: Hybrid 1D-2D Diodes with Engineered Electronic Properties

    KAUST Repository

    Bera, Ashok

    2015-12-28

    Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. ZnO Nanorods on a LaAlO3 -SrTiO3 Interface: Hybrid 1D-2D Diodes with Engineered Electronic Properties.

    Science.gov (United States)

    Bera, Ashok; Lin, Weinan; Yao, Yingbang; Ding, Junfeng; Lourembam, James; Wu, Tom

    2016-02-10

    Integrating nanomaterials with different dimensionalities and properties is a versatile approach toward realizing new functionalities in advanced devices. Here, a novel diode-type heterostructure is reported consisting of 1D semiconducting ZnO nanorods and 2D metallic LaAlO3-SrTiO3 interface. Tunable insulator-to-metal transitions, absent in the individual components, are observed as a result of the competing temperature-dependent conduction mechanisms. Detailed transport analysis reveals direct tunneling at low bias, Fowler-Nordheim tunneling at high forward bias, and Zener breakdown at high reverse bias. Our results highlight the rich electronic properties of such artificial diodes with hybrid dimensionalities, and the design principle may be generalized to other nanomaterials.

  2. Pressure effects on the 2D electron system in LaAlO{sub 3}/SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Borisov, Vladislav; Jeschke, Harald O.; Valenti, Roser [Institute of Theoretical Physics, Goethe University, D-60438 Frankfurt am Main (Germany); Zabaleta, Jone [Max Planck Institute for Solid State Research, D-70569 Stuttgart (Germany); Kopp, Thilo [Center for Electronic Correlations and Magnetism, Experimental Physics VI, Institute of Physics, University of Augsburg, D-86135 Augsburg (Germany)

    2016-07-01

    We present a theoretical study of pressure effects on the electronic properties of the LaAlO{sub 3}/SrTiO{sub 3} (001) interface. Lattice relaxation plays a crucial role for the formation of the 2D electron system (2DES), in agreement with previous reports. We observe that the carrier density of the 2DES at zero pressure is much lower than the ''polar catastrophe'' estimate of 0.5 e{sup -} per two-dimensional unit cell, which agrees with most experimental works. Under hydrostatic pressure, structural distortions in LaAlO{sub 3} (LAO) are largely suppressed, whereas they increase in SrTiO{sub 3} (STO), and the carrier density of the 2DES is enhanced by almost 45% using a moderate pressure of 4.1 GPa. The origin of this behavior as well as the explanation for the low carrier density at the interface at ambient pressure are discussed in terms of the lattice polarization and electronic Berry phase in the LAO oxide. Reduction of the calculated static dielectric constants of LAO and STO under pressure might account for the recent experimental findings regarding the carrier mobility.

  3. Quenching Plasma Waves in Two Dimensional Electron Gas by a Femtosecond Laser Pulse

    Science.gov (United States)

    Shur, Michael; Rudin, Sergey; Greg Rupper Collaboration; Andrey Muraviev Collaboration

    Plasmonic detectors of terahertz (THz) radiation using the plasma wave excitation in 2D electron gas are capable of detecting ultra short THz pulses. To study the plasma wave propagation and decay, we used femtosecond laser pulses to quench the plasma waves excited by a short THz pulse. The femtosecond laser pulse generates a large concentration of the electron-hole pairs effectively shorting the 2D electron gas channel and dramatically increasing the channel conductance. Immediately after the application of the femtosecond laser pulse, the equivalent circuit of the device reduces to the source and drain contact resistances connected by a short. The total response charge is equal to the integral of the current induced by the THz pulse from the moment of the THz pulse application to the moment of the femtosecond laser pulse application. This current is determined by the plasma wave rectification. Registering the charge as a function of the time delay between the THz and laser pulses allowed us to follow the plasmonic wave decay. We observed the decaying oscillations in a sample with a partially gated channel. The decay depends on the gate bias and reflects the interplay between the gated and ungated plasmons in the device channel. Army Research Office.

  4. Averaged spacing and 2-d organization of collagen fibrils in the posterior cornea of the rabbit eye assessed by transmission electron microscopy.

    Science.gov (United States)

    Doughty, Michael J

    2014-04-01

    To assess how reproducible collagen fibril spacing might be in the corneal stroma as viewed by transmission electron microscopy by calculating averaged values for the 2-D organization. One cornea from 8 albino rabbits (2 kg) was fixed in situ to preserve natural shape. Thin sections were stained with 2% phosphotungstic acid (PTA) and images taken of fibrils from the central-posterior stroma. After projection at 250,000 X magnification, an overlay was prepared of the fibrils. Using a 500 × 500 nm region of interest (ROI), the distances to all fibril centers were measured to 2 nm resolution. The sets of fibrils had average diameters between 32.4 and 36.1 nm (group mean ± SD of 34.4 ± 4.2 nm). The mean fibril density was 396 ± 21 per square micrometer, with a fibril area fraction of 38.7 ± 3.9%. The mean distance to the literal nearest neighbor fibril center was 43.2 ± 4.5 nm. A radial distribution analysis showed a distinct nearest neighbors peak at 51 nm. This nearest neighbors peak had an average amplitude of 2.236 ± 0.315, with a broader secondary peak being evident in all data sets centered at 93 nm with an average amplitude of 1.166 ± 0.093 (or 53.3 ± 7.1% of the nearest neighbors peak). Overall, these results show that a predictable 2-D organization can be demonstrated for collagen fibrils in rabbit corneas when consideration is given to sample selection and preparation and the image analysis strategy.

  5. Gas Electron Multiplier detectors with high reliability and stability

    CERN Document Server

    Ovchinnikov, B M; Ovchinnikov, Yu B

    2010-01-01

    The Gas Electron Multiplier detectors with wire and metallic electrodes, with a gas filling in the gap between them were proposed and tested. The main advantage of these Gas Electron Multipliers compared to standard ones consists in their increased stability and reliability. The experimental results on testing of such detectors with gaps between the electrodes of 1 and 3 mm are reported. It is demonstrated, that the best gas filling for the gas electron multipliers is neon with small admixture of quenching gases (for example, (N2+H2O) at ~100ppm). This filling offers the greatest coefficient of proportional multiplication as compared with other gases, at small electric potential difference between the GEM electrodes, in absence of streamer discharges in the proportional region. The results on operation of the multi-channel gas electron multiplier with wire cathode and continuous anode filled with Ne, Ar, Ar+CH4 and Ar+1%Xe are presented also. Based on the experimental observations, the explanation of the mech...

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

    Directory of Open Access Journals (Sweden)

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  9. An electronic nose for quantitative determination of gas concentrations

    Science.gov (United States)

    Jasinski, Grzegorz; Kalinowski, Paweł; Woźniak, Łukasz

    2016-11-01

    The practical application of human nose for fragrance recognition is severely limited by the fact that our sense of smell is subjective and gets tired easily. Consequently, there is considerable need for an instrument that can be a substitution of the human sense of smell. Electronic nose devices from the mid 1980s are used in growing number of applications. They comprise an array of several electrochemical gas sensors with partial specificity and a pattern recognition algorithms. Most of such systems, however, is only used for qualitative measurements. In this article usage of such system in quantitative determination of gas concentration is demonstrated. Electronic nose consist of a sensor array with eight commercially available Taguchi type gas sensor. Performance of three different pattern recognition algorithms is compared, namely artificial neural network, partial least squares regression and support vector machine regression. The electronic nose is used for ammonia and nitrogen dioxide concentration determination.

  10. Fully automated, gas sensing, and electronic parameter measurement setup for miniaturized nanoparticle gas sensors

    Science.gov (United States)

    Kennedy, M. K.; Kruis, F. E.; Fissan, H.; Mehta, B. R.

    2003-11-01

    In this study, a measurement setup has been designed and fabricated for the measurement of gas sensor characteristics and electronic parameters of nanostructured thin layers in the temperature range from room temperature to 450 °C in controlled gas environments. The setup consists of: (i) a gas environment chamber, (ii) a specially designed substrate and substrate holder, and (iii) control, supply, and measurement electronics. The buried geometry of the contacts is specially designed for the deposition of nanoparticles from the gas phase to guarantee uniform thin layers, and the setup can be used to make measurement on high resistivity (1010 Ω cm) nanoparticle samples. The gas inlet, operating temperature, and electronic control of the measurement system are automated by means of a personal computer. Coupling the measurements of interdependent gas sensing and electronic parameters at identical conditions, in a single setup encompassing a wide range of sensing gas levels and substrate temperatures, makes this system ideally suited for carrying out multiple measurements required for optimizing sensor configuration and understanding the size-dependent properties of nanoparticle sensors.

  11. High Temperature Electron Localization in dense He Gas

    CERN Document Server

    Borghesani, A F

    2002-01-01

    We report new accurate mesasurements of the mobility of excess electrons in high density Helium gas in extended ranges of temperature $[(26\\leq T\\leq 77) K ]$ and density $[ (0.05\\leq N\\leq 12.0) {atoms} \\cdot {nm}^{-3}]$ to ascertain the effect of temperature on the formation and dynamics of localized electron states. The main result of the experiment is that the formation of localized states essentially depends on the relative balance of fluid dilation energy, repulsive electron-atom interaction energy, and thermal energy. As a consequence, the onset of localization depends on the medium disorder through gas temperature and density. It appears that the transition from delocalized to localized states shifts to larger densities as the temperature is increased. This behavior can be understood in terms of a simple model of electron self-trapping in a spherically symmetric square well.

  12. The Gas Electron Multiplier Chamber Exhibition LEPFest 2000

    CERN Multimedia

    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

  13. Coherent electron focusing with quantum point contacts in a two-dimensional electron gas

    NARCIS (Netherlands)

    Houten, H. van; Beenakker, C.W.J.; Williamson, J.G.; Broekaart, M.E.I.; Loosdrecht, P.H.M. van; Wees, B.J. van; Mooij, J.E.; Foxon, C.T.; Harris, J.J.

    1989-01-01

    Transverse electron focusing in a two-dimensional electron gas is investigated experimentally and theoretically for the first time. A split Schottky gate on top of a GaAs-AlxGa1–xAs heterostructure defines two point contacts of variable width, which are used as injector and collector of ballistic el

  14. CHEM2D-OPP: A New Linearized Gas-Phased Ozone Photochemistry Parameterization for HIih-Altitude NWP and Climate Models

    Science.gov (United States)

    2006-01-01

    oxygen losses, through re- actions involving the NOx, ClOx, HOx, and BrOx families and long-lived constituents. The spatial and temporal dis- tributions... clima - www.atmos-chem-phys.net/6/4943/2006/ Atmos. Chem. Phys., 6, 4943–4972, 2006 4968 J. P. McCormack et al.: CHEM2D-OPP linearized ozone

  15. Electron gas induced in SrTiO3

    Science.gov (United States)

    Fu, Han; Reich, K. V.; Shklovskii, B. I.

    2016-03-01

    This mini-review is dedicated to the 85th birthday of Prof. L.V. Keldysh, from whom we have learned so much. In this paper, we study the potential and electron density depth profiles in surface accumulation layers in crystals with a large and nonlinear dielectric response such as SrTiO3 (STO) in the cases of planar, spherical, and cylindrical geometries. The electron gas can be created by applying an induction D 0 to the STO surface. We describe the lattice dielectric response of STO using the Landau-Ginzburg free energy expansion and employ the Thomas-Fermi (TF) approximation for the electron gas. For the planar geometry, we arrive at the electron density profile n( x) ∝ ( x + d)-12/7, where d ∝ D 0 -12/7 . We extend our results to overlapping electron gases in GTO/STO/GTO heterojunctions and electron gases created by spill-out from NSTO (heavily n-type doped STO) layers into STO. Generalization of our approach to a spherical donor cluster creating a big TF atom with electrons in STO brings us to the problem of supercharged nuclei. It is known that for an atom with a nuclear charge Ze where Z > 170, electrons collapse onto the nucleus, resulting in a net charge Zn physics, the collapse is caused by the nonlinear dielectric response. Electrons collapse into the charged spherical donor cluster with radius R when its total charge number Z exceeds the critical value Z c ≈ R/ a, where a is the lattice constant. The net charge e Z n grows with Z until Z exceeds Z* ≈ ( R/ a)9/7. After this point, the charge number of the compact core Z n remains ≈ Z*, with the rest Z* electrons forming a sparse TF atom with it. We extend our studies of collapse to the case of long cylindrical clusters as well.

  16. Assessment of a 2D electronic portal imaging devices-based dosimetry algorithm for pretreatment and in-vivo midplane dose verification

    Directory of Open Access Journals (Sweden)

    Ali Jomehzadeh

    2016-01-01

    Conclusion: The 2D EPID-based dosimetry algorithm provides an accurate method to verify the dose of a simple 10 × 10 cm2 field, in two dimensions, inside a homogenous slab phantom and an IMRT prostate plan, as well as in 3D conformal plans (prostate, head-and-neck, and lung plans applied using an anthropomorphic phantom and in vivo. However, further investigation to improve the 2D EPID dosimetry algorithm for a head-and-neck case, is necessary.

  17. A First Mass Production of Gas Electron Multipliers

    CERN Document Server

    Barbeau, P S; Geissinger, J D; Miyamoto, J; Shipsey, I; Yang, R

    2003-01-01

    We report on the manufacture of a first batch of approximately 2,000 Gas Electron Multipliers (GEMs) using 3M's fully automated roll to roll flexible circuit production line. This process allows low-cost, reproducible fabrication of a high volume of GEMs of dimensions up to 30$\\times$30 cm$^{2}$. First tests indicate that the resulting GEMs have optimal properties as radiation detectors. Production techniques and preliminary measurements of GEM performance are described. This now demonstrated industrial capability should help further establish the prominence of micropattern gas detectors in accelerator based and non-accelerator particle physics, imaging and photodetection.

  18. 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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Substitutionally doped phosphorene: electronic properties and gas sensing

    Science.gov (United States)

    Suvansinpan, Nawat; Hussain, Fayyaz; Zhang, Gang; Hsin Chiu, Cheng; Cai, Yongqing; Zhang, Yong-Wei

    2016-02-01

    Phosphorene, a new elemental two-dimensional material, has attracted increasing attention owing to its intriguing electronic properties. In particular, pristine phospohorene, due to its ultrahigh surface-volume ratio and high chemical activity, has been shown to be promising for gas sensing (Abbas et al 2015 ACS Nano 9 5618). To further enhance its sensing ability, we perform first-principles calculations based on density functional theory to study substitutionally doped phosphorene with 17 different atoms, focusing on structures, energetics, electronic properties and gas sensing. Our calculations reveal that anionic X (X = O, C and S) dopants have a large binding energy and highly dispersive electronic states, signifying the formation of covalent X-P bonds and thus strong structural stability. Alkali atom (Li and Na) doping is found to donate most of the electrons in the outer s-orbital by forming ionic bonds with P, and the band gap decreases by pushing down the conduction band, suggesting that the optical and electronic properties of the doped phosphorene can be tailored. For doping with VIIIB-group (Fe, Co and Ni) elements, a strong affinity is predicted and the binding energy and charge transfer are correlated strongly with their electronegativity. By examining NO molecule adsorption, we find that these metal doped phosphorenes (MDPs) in general exhibit a significantly enhanced chemical activity compared with pristine phosphorene. Our study suggests that substitutionally doped phosphorene shows many intriguing electronic and optic properties different from pristine phosphorene and MDPs are promising in chemical applications involving molecular adsorption and desorption processes, such as materials growth, catalysis, gas sensing and storage.

  20. Heavy-Ion-Induced Electronic Desorption of Gas from Metals

    CERN Document Server

    Molvik, A W; Mahner, E; Kireeff Covo, M; Bellachioma, M C; Bender, M; Bieniosek, F M; Hedlund, E; Krämer, A; Kwan, J; Malyshev, O B; Prost, L; Seidl, P A; Westenskow, G; Westerberg, L

    2007-01-01

    During heavy-ion operation in several particle accelerators worldwide, 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 (dEe/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering.

  1. Heavy-ion induced electronic desorption of gas from metals

    Energy Technology Data Exchange (ETDEWEB)

    Molvik, A W; Kollmus, H; Mahner, E; Covo, M K; Bellachioma, M C; Bender, M; Bieniosek, F M; Hedlund, E; Kramer, A; Kwan, J; Malyshev, O B; Prost, L; Seidl, P A; Westenskow, G; Westerberg, L

    2006-12-19

    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}/d/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering.

  2. The gas electron multiplier (GEM): Operating principles and applications

    Science.gov (United States)

    Sauli, Fabio

    2016-01-01

    Introduced by the author in 1997, The Gas Electron Multiplier (GEM) constitutes a powerful addition to the family of fast radiation detectors; originally developed for particle physics experiments, the device and has spawned a large number of developments and applications; a web search yields more than 400 articles on the subject. This note is an attempt to summarize the status of the design, developments and applications of the new detector.

  3. Perspectives for spintronics in 2D materials

    Directory of Open Access Journals (Sweden)

    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.

  4. Computational 2D Materials Database

    DEFF Research Database (Denmark)

    Rasmussen, Filip Anselm; Thygesen, Kristian Sommer

    2015-01-01

    We present a comprehensive first-principles study of the electronic structure of 51 semiconducting monolayer transition-metal dichalcogenides and -oxides in the 2H and 1T hexagonal phases. The quasiparticle (QP) band structures with spin-orbit coupling are calculated in the G(0)W(0) approximation...... and used as input to a 2D hydrogenic model to estimate exciton binding energies. Throughout the paper we focus on trends and correlations in the electronic structure rather than detailed analysis of specific materials. All the computed data is available in an open database....

  5. c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 gas-phase lines

    CERN Document Server

    Lahuis, Fred; 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 ~20% respectively ~9% of our sources. The observed [Ne II] line fluxes and upper limits are consistent with [Ne II] excitation in an X-ray irradiated disk around stars with X-ray luminosities L_X=10^{29}-10^{31} erg s^{-1}. [Fe I] is detected at ~10^-5-10^-4 L_Sun, but no [S I] or [Fe II] is detected down to ~10^{-6} L_Sun. The [Fe I] detections indicate the presence of gas-rich disks with masses of >~0.1 M_J. No H_2 0-0 S(0) and S(1) disk emission is detected, except for S(1) toward one source. These data give upper limits on the warm (T~100-200K) gas mass of a few Jovian masses, consistent with recent T Tauri disk models which include gas heating by stellar radiation. Compact disk emission of hot (T>~500K) gas is observed through the H_2 0-0...

  6. Design and function of an electron mobility spectrometer with a thick gas electron multiplier

    Energy Technology Data Exchange (ETDEWEB)

    Orchard, Gloria M., E-mail: gloria.spirou@gmail.com [Faculty of Energy Systems and Nuclear Science, University of Ontario Institute of Technology, Oshawa, Ontario, Canada, L1H 7K4 (Canada); Puddu, Silvia [CERN, 1211 Geneva 23, Switzerland and University of Bern, LHEP, Sidlerstrasse 5, 3012 Bern (Switzerland); Waker, Anthony J., E-mail: anthony.waker@uoit.ca [Faculty of Energy Systems and Nuclear Science, University of Ontario Institute of Technology, Oshawa, Ontario, Canada, L1H 7K4 (Canada)

    2016-04-11

    The design and function of an electron mobility spectrometer (EMS) including a thick gas electron multiplier (THGEM) is presented. The THGEM was designed to easily be incorporated in an existing EMS to investigate the ability to detect tritium in air using a micropattern gas detector. The THGEM and a collection plate (anode) were installed and the appropriate circuitry was designed and connected to supply the required voltages to the THGEM-EMS. An alpha source ({sup 241}Am) was used to generate electron-ion pairs within the gas-filled sensitive volume of the EMS. The electrons were used to investigate the THGEM-EMS response as a function of applied voltage to the THGEM and anode. The relative gas-gain and system resolution of the THGEM-EMS were measured at various applied voltage settings. It was observed a potential difference across the THGEM of +420 V and potential difference across the induction region of +150 V for this EMS setup resulted in the minimum voltage requirements to operate with a stable gain and system resolution. Furthermore, as expected, the gain is strongly affected not only by the potential difference across the THGEM, but also by the applied voltage to the anode and resulting potential difference between the THGEM and anode.

  7. Dipolar quantum electrodynamics of the two-dimensional electron gas

    Science.gov (United States)

    Todorov, Yanko

    2015-03-01

    Similarly to a previous work on the homogeneous electron gas [Y. Todorov, Phys. Rev. B 89, 075115 (2014), 10.1103/PhysRevB.89.075115], we apply the Power-Zienau-Wooley (PZW) formulation of the quantum electrodynamics to the case of an electron gas quantum confined by one-dimensional potential. We provide a microscopic description of all collective plasmon modes of the gas, oscillating both along and perpendicular to the direction of quantum confinement. Furthermore, we study the interaction of the collective modes with a photonic structure, planar metallic waveguide, by using the full expansion of the electromagnetic field into normal modes. We show how the boundary conditions for the electromagnetic field influence both the transverse light-matter coupling and the longitudinal particle-particle interactions. The PZW descriptions appear thus as a convenient tool to study semiconductor quantum optics in geometries where quantum-confined particles interact with strongly confined electromagnetic fields in microresonators, such as the ones used to achieve the ultrastrong light-matter coupling regime.

  8. Long-time tails of the velocity autocorrelation function in 2D and 3D lattice gas cellular automata: a test of mode-coupling theory

    NARCIS (Netherlands)

    Hoef, M.A. van der; Frenkel, D.

    1990-01-01

    We report simulations of the velocity autocorrelation function (VACF) of a tagged particle in two- and three-dimensional lattice-gas cellular automata, using a new technique that is about a million times more efficient than the conventional techniques. The simulations clearly show the algebraic t-D/

  9. 2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence.

    Science.gov (United States)

    Blomberg, Sara; Zhou, Jianfeng; Gustafson, Johan; Zetterberg, Johan; Lundgren, Edvin

    2016-11-16

    In recent years, efforts have been made in catalysis related surface science studies to explore the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. Techniques such as high pressure scanning tunneling/atomic force microscopy (HPSTM/AFM), near ambient pressure x-ray photoemission spectroscopy (NAPXPS), surface x-ray diffraction (SXRD) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at semi-realistic conditions have been used to study the surface structure of model catalysts under reaction conditions, combined with simultaneous mass spectrometry (MS). These studies have provided an increased understanding of the surface dynamics and the structure of the active phase of surfaces and nano particles as a reaction occurs, providing novel information on the structure/activity relationship. However, the surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface. Therefore, the catalytic activity of the sample itself will act as a gas-source or gas-sink, and will affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, we have applied planar laser induced fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts. Our measurements demonstrate that the gas composition differs significantly close to the catalyst and at the position of the MS, which indeed should have a profound effect on the surface structure. However, PLIF applied to catalytic reactions presents several beneficial properties in addition to investigate the effect of the catalyst on the effective gas composition close to the model catalyst. The high spatial and temporal resolution of PLIF provides a unique tool to visualize the on-set of catalytic reactions and to compare different model catalysts in the same reactive environment. The technique can be

  10. 2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence

    Science.gov (United States)

    Blomberg, Sara; Zhou, Jianfeng; Gustafson, Johan; Zetterberg, Johan; Lundgren, Edvin

    2016-11-01

    In recent years, efforts have been made in catalysis related surface science studies to explore the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. Techniques such as high pressure scanning tunneling/atomic force microscopy (HPSTM/AFM), near ambient pressure x-ray photoemission spectroscopy (NAPXPS), surface x-ray diffraction (SXRD) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at semi-realistic conditions have been used to study the surface structure of model catalysts under reaction conditions, combined with simultaneous mass spectrometry (MS). These studies have provided an increased understanding of the surface dynamics and the structure of the active phase of surfaces and nano particles as a reaction occurs, providing novel information on the structure/activity relationship. However, the surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface. Therefore, the catalytic activity of the sample itself will act as a gas-source or gas-sink, and will affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, we have applied planar laser induced fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts. Our measurements demonstrate that the gas composition differs significantly close to the catalyst and at the position of the MS, which indeed should have a profound effect on the surface structure. However, PLIF applied to catalytic reactions presents several beneficial properties in addition to investigate the effect of the catalyst on the effective gas composition close to the model catalyst. The high spatial and temporal resolution of PLIF provides a unique tool to visualize the on-set of catalytic reactions and to compare different model catalysts in the same reactive environment. The technique can be

  11. Industrial demonstration plant for electron beam flue gas treatment

    Science.gov (United States)

    Chmielewski, Andrzej G.; Iller, Edward; Zimek, Zbigniew; Romanowski, Micna; Koperski, Kazimierz

    1995-09-01

    The positive results of the tests performed on laboratory and pilot installations in Poland, Japan, USA and Germany have led to decision concerning design and construction of the industrial demonstration plant for electron beam flue gas treatment. The planned flue gas purification installation will treat tlue gases from a block which consists of two Benson type boilers of power 56 MWe each supplying additional steam for heating purposes up to 40 MWth each. The 270 000 Nm3 /h tlue gases (half of produced by the block) will be treated with efficiency of 90% for SO2 and 70% for NOx. This meets Polish regulations which will be imposed in 1997. The technical and economical description of the project is presented in the paper.

  12. Fermi-liquid behavior of the low-density 2D hole gas in a GaAs/AlGaAs heterostructure at large values of r(s).

    Science.gov (United States)

    Proskuryakov, Y Y; Savchenko, A K; Safonov, S S; Pepper, M; Simmons, M Y; Ritchie, D A

    2001-05-21

    We examine the validity of the Fermi-liquid description of the dilute 2D hole gas in the crossover from "metallic"-to-"insulating" behavior of rho(T). It has been established that, at r(s) as large as 29, negative magnetoresistance does exist and is well described by weak localization theory. The dephasing time, extracted from the magnetoresistance, is dominated by the T2 term due to hole-hole scattering in the clean limit. The effect of hole-hole interactions, however, is suppressed when compared with the theory derived for small r(s).

  13. Qualitative Characterization of the Aqueous Fraction from Hydrothermal Liquefaction of Algae Using 2D Gas Chromatography with Time-of-flight Mass Spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Maddi, Balakrishna; Panisko, Ellen; Albrecht, Karl; Howe, Daniel

    2016-01-01

    Two-dimensional gas chromatography coupled with time of flight mass spectrometry is a powerful tool for identifying and quantifying components in complex mixtures. It has been used to analyze gasoline, jet fuel, diesel, bio-diesel and organic fraction of bio-crude/bio-oil. In these experiments, the first dimension of separation was non-polar, followed by a polar separation. Aqueous fractions of bio-crude and other aqueous samples have been examined with similar column combinations. However, sample preparation techniques such as derivatization, solvent extraction, and solid-phase extraction were necessary prior to analysis. In this study, aqueous fraction obtained from hydrothermal liquefaction of algae was characterized by two-dimensional gas chromatography coupled with time of flight mass spectrometry without prior sample preparation techniques using a polar separation in the first dimension followed by a non-polar separation. Two-dimensional plots from this analysis were compared with those obtained from the more traditional column combination. Results from qualitative characterization aqueous fractions of algal bio-crude are discussed in detail. The advantages of using a polar separation followed by a non-polar separation for characterization of organics in aqueous samples by two-dimensional gas chromatography coupled with time of flight mass spectrometry are highlighted.

  14. Intensity dependence of electron gas kinetics in a laser corona

    Directory of Open Access Journals (Sweden)

    Mašek Martin

    2013-11-01

    Full Text Available In various experimental situations relevant to the laser fusion, such as plasma near the light entrance holes of hohlraum in the indirect drive experiments or more recently in the shock ignition direct drive a relatively long underdense plasma of corona type is encountered, which is subject to an intense nanosecond laser beam. The plasma is only weakly collisional and thus in the electron phase space a complicated kinetic evolution is going on, which is taking the electron gas fairly far from the thermal equilibrium and contributes to its unstable behaviour. These phenomena impede the absorption and thermalization of the incoming laser energy, create groups of fast electrons and also may lead to a non-linear reflection of the heating laser beam. One of the key processes leading to the electron acceleration is the stimulated Raman scattering (SRS in its non-linear phase. The SRS in the presence of electron-ion collisions requires a certain threshold intensity above which the mentioned non-dissipative phenomena can occur and develop to the stage, where they may become unpleasant for the fusion experiments. To assess this intensity limit a computational model has been developed based on the Vlasov-Maxwell kinetics describing such a plasma in 1D geometry. At a relatively high intensity of 1016 W/cm2 a number of non-linear phenomena are predicted by the code such as a saturation of Landau damping, which is then translated in an unfavourable time dependence of the reflected light intensity and formation of accelerated electron groups due to the electron trapping. The purpose of the present contribution is to map the intensity dependence of this non-linear development with the aim of assessing its weight in fusion relevant situations.

  15. Room-Temperature Coherent Optical Phonon in 2D Electronic Spectra of CH3NH3PbI3 Perovskite as a Possible Cooling Bottleneck

    Energy Technology Data Exchange (ETDEWEB)

    Monahan, Daniele M. [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States); Guo, Liang [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States); Lin, Jia [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States); Dou, Letian [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States); Yang, Peidong [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States); Fleming, Graham R. [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kavli Energy NanoSciences Inst. at Berkeley, Berkeley, CA (United States)

    2017-06-29

    A hot phonon bottleneck may be responsible for slow hot carrier cooling in methylammonium lead iodide hybrid perovskite, creating the potential for more efficient hot carrier photovoltaics. In room-temperature 2D electronic spectra near the band edge, we observe in this paper amplitude oscillations due to a remarkably long lived 0.9 THz coherent phonon population at room temperature. This phonon (or set of phonons) is assigned to angular distortions of the Pb–I lattice, not coupled to cation rotations. The strong coupling between the electronic transition and the 0.9 THz mode(s), together with relative isolation from other phonon modes, makes it likely to cause a phonon bottleneck. Finally, the pump frequency resolution of the 2D spectra also enables independent observation of photoinduced absorptions and bleaches independently and confirms that features due to band gap renormalization are longer-lived than in transient absorption spectra.

  16. Image processing of 2D crystal images.

    Science.gov (United States)

    Arheit, Marcel; Castaño-Díez, Daniel; Thierry, Raphaël; Gipson, Bryant R; Zeng, Xiangyan; Stahlberg, Henning

    2013-01-01

    Electron crystallography of membrane proteins uses cryo-transmission electron microscopy to image frozen-hydrated 2D crystals. The processing of recorded images exploits the periodic arrangement of the structures in the images to extract the amplitudes and phases of diffraction spots in Fourier space. However, image imperfections require a crystal unbending procedure to be applied to the image before evaluation in Fourier space. We here describe the process of 2D crystal image unbending, using the 2dx software system.

  17. Electron beam treatment of exhaust gas with high NOx concentration

    Science.gov (United States)

    Licki, Janusz; Chmielewski, Andrzej G.; Pawelec, Andrzej; Zimek, Zbigniew; Witman, Sylwia

    2014-05-01

    Simulated exhaust gases with a high NOx concentration, ranging from 200 to 1700 ppmv, were irradiated by an electron beam from an accelerator. In the first part of this study, only exhaust gases were treated. Low NOx removal efficiencies were obtained for high NOx concentrations, even with high irradiation doses applied. In the second part of study, gaseous ammonia or/and vapor ethanol were added to the exhaust gas before its inlet to the plasma reactor. These additions significantly enhanced the NOx removal efficiency. The synergistic effect of high SO2 concentration on NOx removal was observed. The combination of electron beam treatment with the introduction of the above additions and with the performance of irradiation under optimal parameters ensured high NOx removal efficiency without the application of a solid-state catalyst.

  18. Coupled Cluster Channels in the Homogeneous Electron Gas

    CERN Document Server

    Shepherd, James J; Scuseria, Gustavo E

    2013-01-01

    We discuss diagrammatic modifications to the coupled cluster doubles (CCD) equations, wherein different groups of terms out of rings, ladders, crossed-rings and mosaics can be removed to form approximations to the coupled cluster method, of interest due to their similarity with various types of random phase approximations. The finite uniform electron gas is benchmarked for 14- and 54-electron systems at the complete basis set limit over a wide density range and performance of different flavours of CCD are determined. These results confirm that rings generally overcorrelate and ladders generally undercorrelate; mosaics-only CCD yields a result surprisingly close to CCD. We use a recently developed numerical analysis [J. J. Shepherd and A. Gr\\"uneis, Phys. Rev. Lett. 110, 226401 (2013)] to study the behaviours of these methods in the thermodynamic limit. We determine that the mosaics, on forming the Brueckner Hamltonian, open a gap in the effective one-particle eigenvalues at the Fermi energy. Numerical evidenc...

  19. 2D stellar population and gas kinematics of the inner 1.5 kpc of the post-starburst quasar SDSS J0210-0903

    CERN Document Server

    Sanmartim, David; Brotherton, Michael S

    2012-01-01

    Post-Starburst Quasars (PSQs) are hypothesized to represent a stage in the evolution of massive galaxies in which the star formation has been recently quenched due to the feedback of the nuclear activity. In this paper our goal is to test this scenario with a resolved stellar population study of the PSQ J0210-0903, as well as of its emitting gas kinematics and excitation. We have used optical Integral Field Spectroscopy obtained with the Gemini GMOS instrument at a velocity resolution of ~120 km/s and spatial resolution of ~0.5 kpc. We find that old stars dominate the luminosity (at 4700 \\AA) in the inner 0.3 kpc (radius), while beyond this region (at ~0.8 kpc) the stellar population is dominated by both intermediate age and young ionizing stars. The gas emission-line ratios are typical of Seyfert nuclei in the inner 0.3 kpc, where an outflow is observed. Beyond this region the line ratios are typical of LINERs and may result from the combination of diluted radiation from the nucleus and ionization from young...

  20. Peculiarities of the C2d3Π→a3Π band system intensities in gas discharges through CO-contained mixtures

    Science.gov (United States)

    Grigorian, G. M.

    2012-12-01

    The paper discusses the experimental results pointing to the efficient channel of the CO vibrational to the C2 electronic energy-transfer. The radiation spectra of the d3Πg electronic state of C2 molecule are investigated and the relation of their kinetics to a vibrational excitation of CO molecules in the He-CO-O2 plasma is discussed. The changes of CO vibrational energy distribution (VED) were imposed by an application of a laser resonator to the discharge tube under investigation. It was found that the modulation of laser radiation (and VED) led to a similar changes of the spontaneous radiation from d3Πg state of C2 molecules

  1. PIC code modeling of spacecraft charging potential during electron beam injection into a background of neutral gas and plasma, part 1

    Science.gov (United States)

    Koga, J. K.; Lin, C. S.; Winglee, R. M.

    1989-01-01

    Injections of nonrelativistic electron beams from an isolated equipotential conductor into a uniform background of plasma and neutral gas were simulated using a 2-D electrostatic particle code. The ionization effects on spacecraft charging are examined by including interactions of electrons with neutral gas. The simulations show that the conductor charging potential decreases with increasing neutral background density due to the production of secondary electrons near the conductor surface. In the spacecraft wake, the background electrons accelerated towards the charged spacecraft produce an enhancement of secondary electrons and ions. Simulations run for longer times indicate that the spacecraft potential is further reduced and short wavelength beam-plasma oscillations appear. The results are applied to explain the spacecraft charging potential measured during the SEPAC experiments from Spacelab 1.

  2. Quantum holographic encoding in a two-dimensional electron gas

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Christopher

    2010-05-26

    The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.

  3. High-Temperature Gas Sensor Array (Electronic Nose) Demonstrated

    Science.gov (United States)

    Hunter, Gary W.

    2002-01-01

    The ability to measure emissions from aeronautic engines and in commercial applications such as automotive emission control and chemical process monitoring is a necessary first step if one is going to actively control those emissions. One single sensor will not give all the information necessary to determine the chemical composition of a high-temperature, harsh environment. Rather, an array of gas sensor arrays--in effect, a high-temperature electronic "nose"--is necessary to characterize the chemical constituents of a diverse, high-temperature environment, such as an emissions stream. The signals produced by this nose could be analyzed to determine the constituents of the emission stream. Although commercial electronic noses for near-room temperature applications exist, they often depend significantly on lower temperature materials or only one sensor type. A separate development effort necessary for a high-temperature electronic nose is being undertaken by the NASA Glenn Research Center, Case Western Reserve University, Ohio State University, and Makel Engineering, Inc. The sensors are specially designed for hightemperature environments. A first-generation high-temperature electronic nose has been demonstrated on a modified automotive engine. This nose sensor array was composed of sensors designed for hightemperature environments fabricated using microelectromechanical-systems- (MEMS-) based technology. The array included a tin-oxide-based sensor doped for nitrogen oxide (NOx) sensitivity, a SiC-based hydrocarbon (CxHy) sensor, and an oxygen sensor (O2). These sensors operate on different principles--resistor, diode, and electrochemical cell, respectively--and each sensor has very different responses to the individual gases in the environment. A picture showing the sensor head for the array is shown in the photograph on the left and the sensors installed in the engine are shown in the photograph on the right. Electronics are interfaced with the sensors for

  4. Flue gas dry scrubbing using pulsed electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Penetrante, B.M.

    1996-02-20

    Electron beam dry scrubbing is a technique for removing in a single step both nitrogen oxides (NO{sub x}) and sulfur dioxide (SO{sub 2}) from the off-gas generated by utilities burning high sulfur coal. The use of pulsed electron beams may provide the most cost-effective solution to the implementation of this technique. This paper presents the results of plasma chemistry calculations to study the effect of dose rate, pulse length and pulse repetition rate on pulsed electron beam processing of NO{sub x} and SO{sub 2} in flue gases. The main objective is to determine if the proposed combinations of dose rate, pulse length and pulse repetition rate would have any deleterious effect on the utilization of radicals for pollutant removal. For a dose rate of 2x10{sup 5} megarads per second and a pulse length of 30 nanoseconds, the average dose per pulse is sufficiently low to prevent any deleterious effect on process efficiency because of radical-radical recombination reactions. During each post-pulse period, the radicals are utilized in the oxidation of NO{sub x} and SO{sub 2} in a timescale of around 200 microseconds; thus, with pulse frequencies of around 5 kilohertz or less, the radical concentrations remain sufficiently low to prevent any significant competition between radical-pollutant and radical-radical reactions. The main conclusion is that a pulsed electron beam reactor, operating with a dose rate of 2x10{sup 5} megarads per second, pulse length of 30 ns and pulse repetition rate of up to around 5 kHz, will have the same plasma chemistry efficiency as an electron beam reactor operating with a very low dose rate in continuous mode.

  5. Evaluation of super-resolution performance of the K2 electron-counting camera using 2D crystals of aquaporin-0.

    Science.gov (United States)

    Chiu, Po-Lin; Li, Xueming; Li, Zongli; Beckett, Brian; Brilot, Axel F; Grigorieff, Nikolaus; Agard, David A; Cheng, Yifan; Walz, Thomas

    2015-11-01

    The K2 Summit camera was initially the only commercially available direct electron detection camera that was optimized for high-speed counting of primary electrons and was also the only one that implemented centroiding so that the resolution of the camera can be extended beyond the Nyquist limit set by the physical pixel size. In this study, we used well-characterized two-dimensional crystals of the membrane protein aquaporin-0 to characterize the performance of the camera below and beyond the physical Nyquist limit and to measure the influence of electron dose rate on image amplitudes and phases.

  6. Monte Carlo model for electron degradation in xenon gas

    CERN Document Server

    Mukundan, Vrinda

    2016-01-01

    We have developed a Monte Carlo model for studying the local degradation of electrons in the energy range 9-10000 eV in xenon gas. Analytically fitted form of electron impact cross sections for elastic and various inelastic processes are fed as input data to the model. Two dimensional numerical yield spectrum, which gives information on the number of energy loss events occurring in a particular energy interval, is obtained as output of the model. Numerical yield spectrum is fitted analytically, thus obtaining analytical yield spectrum. The analytical yield spectrum can be used to calculate electron fluxes, which can be further employed for the calculation of volume production rates. Using yield spectrum, mean energy per ion pair and efficiencies of inelastic processes are calculated. The value for mean energy per ion pair for Xe is 22 eV at 10 keV. Ionization dominates for incident energies greater than 50 eV and is found to have an efficiency of 65% at 10 keV. The efficiency for the excitation process is 30%...

  7. Preparation of cultured cells using high-pressure freezing and freeze substitution for subsequent 2D or 3D visualization in the transmission electron microscope.

    Science.gov (United States)

    Hawes, Philippa C

    2015-01-01

    Transmission electron microscopy (TEM) is an invaluable technique used for imaging the ultrastructure of samples and it is particularly useful when determining virus-host interactions at a cellular level. The environment inside a TEM is not favorable for biological material (high vacuum and high energy electrons). Also biological samples have little or no intrinsic electron contrast, and rarely do they naturally exist in very thin sheets, as is required for optimum resolution in the TEM. To prepare these samples for imaging in the TEM therefore requires extensive processing which can alter the ultrastructure of the material. Here we describe a method which aims to minimize preparation artifacts by freezing the samples at high pressure to instantaneously preserve ultrastructural detail, then rapidly substituting the ice and infiltrating with resin to provide a firm matrix which can be cut into thin sections for imaging. Thicker sections of this material can also be imaged and reconstructed into 3D volumes using electron tomography.

  8. 2D semiconductor optoelectronics

    Science.gov (United States)

    Novoselov, Kostya

    The advent of graphene and related 2D materials has recently led to a new technology: heterostructures based on these atomically thin crystals. The paradigm proved itself extremely versatile and led to rapid demonstration of tunnelling diodes with negative differential resistance, tunnelling transistors, photovoltaic devices, etc. By taking the complexity and functionality of such van der Waals heterostructures to the next level we introduce quantum wells engineered with one atomic plane precision. Light emission from such quantum wells, quantum dots and polaritonic effects will be discussed.

  9. Long-Lived Vortex Structures in Collisional Pure and Gas-Discharge Nonneutral Electron Plasmas

    OpenAIRE

    Kervalishvili, N. A.

    2013-01-01

    The analysis of experimental investigations of equilibrium, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas during the time much more than the electron-neutral collision time has been carried out. The problem of long confinement of the column of pure electron plasma in Penning-Malmberg trap is considered. The mechanism of stability of long-lived vortex structure in gas-discharge nonneutral electron plasma is investigated. The collap...

  10. Extension of the approximate two-dimensional electron gas formulation

    Science.gov (United States)

    Pierret, R. F.

    1985-07-01

    The functional two-dimensional electron gas (2DEG) formalism employed in the analysis of modulation-doped field-effect transistors is extended to properly account for the bulk charge and to more accurately model sub- and near-threshold behavior. The implemented changes basically transform the functional formulation from an above-threshold formalism for lightly doped structures to one of additional utility which automatically approaches expected limits under widely divergent conditions. Sample computations of the surface carrier concentration, relevant energy level positionings, and the semiconductor depletion width as a function of surface potential and doping are also presented and examined. These computations exhibit the general utility of the extended theory and provide an indirect evaluation of the standard two-level 2DEG theory.

  11. Aging measurements with the gas electron multiplier (GEM)

    CERN Document Server

    Altunbas, M C; Kappler, S; Ketzer, B; Ropelewski, Leszek; Sauli, Fabio; Simon, F

    2003-01-01

    Continuing previous aging measurements with detectors based on the Gas Electron Multiplier (GEM), a $31\\times 31$cm$^2$ triple-GEM detector, as used in the small area tracking of the COMPASS experiment at CERN, was investigated. With a detector identical to those installed in the experiment, long-term, high-rate exposures to $8.9$keV X-ray radiation were performed to study its aging properties. In standard operation conditions, with Ar:CO$_2$ (70:30) filling and operated at an effective gain of $8.5\\cdot 10^3$, no change in gain and energy resolution is observed after collecting a total charge of 7mC/mm$^2$, corresponding to seven years of normal operation. This observation confirms previous results demonstrating the relative insensitivity of GEM detectors to aging, even when manufactured with common materials.

  12. 77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

    Science.gov (United States)

    2012-02-22

    ... AGENCY 40 CFR Part 98 RIN 2060-AR09 Greenhouse Gas Reporting Program: Electronics Manufacturing... category of the Greenhouse Gas Reporting Rule related to fluorinated heat transfer fluids. More... INFORMATION CONTACT: Carole Cook, Climate Change Division, Office of Atmospheric Programs...

  13. Environmental Screening Effects in 2D Materials: Renormalization of the Bandgap, Electronic Structure, and Optical Spectra of Few-Layer Black Phosphorus.

    Science.gov (United States)

    Qiu, Diana Y; da Jornada, Felipe H; Louie, Steven G

    2017-08-09

    Few-layer black phosphorus has recently emerged as a promising 2D semiconductor, notable for its widely tunable bandgap, highly anisotropic properties, and theoretically predicted large exciton binding energies. To avoid degradation, it has become common practice to encapsulate black phosphorus devices. It is generally assumed that this encapsulation does not qualitatively affect their optical properties. Here, we show that the contrary is true. We have performed ab initio GW and GW plus Bethe-Salpeter equation (GW-BSE) calculations to determine the quasiparticle (QP) band structure and optical spectrum of one-layer (1L) through four-layer (4L) black phosphorus, with and without encapsulation between hexagonal boron nitride and sapphire. We show that black phosphorus is exceptionally sensitive to environmental screening. Encapsulation reduces the exciton binding energy in 1L by as much as 70% and completely eliminates the presence of a bound exciton in the 4L structure. The reduction in the exciton binding energies is offset by a similarly large renormalization of the QP bandgap so that the optical gap remains nearly unchanged, but the nature of the excited states and the qualitative features of the absorption spectrum change dramatically.

  14. Two-dimensional electron gas in the regime of strong light-matter coupling: Dynamical conductivity and all-optical measurements of Rashba and Dresselhaus coupling

    Science.gov (United States)

    Yudin, Dmitry; Shelykh, Ivan A.

    2016-10-01

    A nonperturbative interaction of an electronic system with a laser field can substantially modify its physical properties. In particular, in two-dimensional (2D) materials with a lack of inversion symmetry, the achievement of a regime of strong light-matter coupling allows direct optical tuning of the strength of the Rashba spin-orbit interaction (SOI). Capitalizing on these results, we build a theory of the dynamical conductivity of a 2D electron gas with both Rashba and Dresselhaus SOIs coupled to an off-resonant high-frequency electromagnetic wave. We argue that strong light-matter coupling modifies qualitatively the dispersion of the electrons and can be used as a powerful tool to probe and manipulate the coupling strengths and adjust the frequency range where optical conductivity is essentially nonzero.

  15. Long-Lived Vortex Structures in Collisional Pure and Gas-Discharge Nonneutral Electron Plasmas

    CERN Document Server

    Kervalishvili, N A

    2013-01-01

    The analysis of experimental investigations of equilibrium, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas during the time much more than the electron-neutral collision time has been carried out. The problem of long confinement of the column of pure electron plasma in Penning-Malmberg trap is considered. The mechanism of stability of long-lived vortex structure in gas-discharge nonneutral electron plasma is investigated. The collapse of electron sheath in gas-discharge nonneutral electron plasma in Penning cell at high pressures of neutral gas is described. The interaction between the stable vortex structure and the annular electron sheath, and the action of vortex structures on the transport of electrons along and across the magnetic field are discussed.

  16. Ferroelectric control of two dimensional electron gas in oxide heterointerface

    Science.gov (United States)

    Thanh, Tra Vu; Chen, Jhih-Wei; Yeh, Chao-Hui; Chen, Yi-Chun; Wu, Chung-Lin; Lin, Jiunn Yuan; Chu, Ying-Hao

    2012-02-01

    Oxide heterointerfaces are emerging as one of the most exciting materials systems in condensed-matter science. One remarkable example is the LaAlO3 /SrTiO3 (LAO/STO) interface, a model system in which a highly mobile electron gas forms between two band insulators. Our study to manipulate the conductivity at this interface by using ferroeletricity of Pb(Zr,Ti)O3. Our transport data strongly suggests that down polarization direction depletes the conducting interface of LAO/STO. After switching the polarization direction (up), it becomes accumulation. In addition, our experiments show there is obvious the band structure changed by cross-sectional scanning tunneling microscopy and combining with X-ray photoelectron spectroscopy (XPS) measurements. The transport properties are measured to build up the connection between macroscopic properties and local electronic structures that have been applied to study this structure. Controlling the conductivity of this oxide interface suggests that this technique may not only extend more generally to other oxide systems but also open much potential to ferroelectric field effect transistors.

  17. The Diamagnetic Phase Transition of Dense Electron Gas: Astrophysical Applications

    Science.gov (United States)

    Wang, Zhaojun; Lü, Guoliang; Zhu, Chunhua; Wu, Baoshan

    2016-10-01

    Neutron stars are ideal astrophysical laboratories for testing theories of the de Haas-van Alphen effect and diamagnetic phase transition which is associated with magnetic domain formation. The “magnetic interaction” between delocalized magnetic moments of electrons (the Shoenberg effect), can result in an effect of the diamagnetic phase transition into domains of alternating magnetization (Condon's domains). Associated with the domain formation are prominent magnetic field oscillation and anisotropic magnetic stress which may be large enough to fracture the crust of magnetar with a super-strong field. Even if the fracture is impossible as in “low-field” magnetar, the depinning phase transition of domain wall (DW) motion driven by low field rate (mainly due to the Hall effect) in the randomly perturbed crust can result in a catastrophically variation of magnetic field. This intermittent motion, similar to the avalanche process, makes the Hall effect be dissipative. These qualitative consequences about magnetized electron gas are consistent with observations of magnetar emission, and especially the threshold critical dynamics of driven DW can partially overcome the difficulties of “low-field” magnetar bursts and the heating mechanism of transient, or “outbursting” magnetar.

  18. Development and testing of a deuterium gas target assembly for neutron production via the H-2(d,n)He-3 reaction at a low-energy accelerator facility

    Energy Technology Data Exchange (ETDEWEB)

    Feautrier, D.; Smith, D.L.

    1992-03-01

    This report describes the development and testing of a deuterium gas target intended for use at a low-energy accelerator facility to produce neutrons for basic research and various nuclear applications. The principle source reaction is H-2(d,n)He-3. It produces a nearly mono-energetic group of neutrons. However, a lower-energy continuum neutron spectrum is produced by the H-2(d;n,p)H-2 reaction and also by deuterons which strike various components in the target assembly. The present target is designed to achieve the following objectives: (1) minimize unwanted background neutron production from the target assembly, (2) provide a relatively low level of residual long-term activity within the target components, (3) have the capacity to dissipate up to 150 watts of beam power with good target longevity, and (4) possess a relatively modest target mass in order to minimize neutron scattering from the target components. The basic physical principles that have to be considered in designing an accelerator target are discussed and the major engineering features of this particular target design are outlined. The results of initial performance tests on this target are documented and some conclusions concerning the viability of the target design are presented.

  19. Quantum interference and spin-orbit effects in the heterostructure with the 2D hole gas in the Si sub 0 sub . sub 2 Ge sub 0 sub . 8 quantum well

    CERN Document Server

    Andrievskij, V V; Komnik, Y F; Mironov, M; Mironov, O A; Whall, T E

    2003-01-01

    The magnetic field (approx 110 kOe)dependences of resistance of the Si sub 0 sub . sub 7 Ge sub 0 sub . sub 3 /Si sub 0 sub . sub 2 Ge sub 0 sub . sub 8 /Si sub 0 sub . sub 7 Ge sub 0 sub . sub 3 heterostructure with a 2D hole gas in the Si sub 0 sub . sub 2 Ge sub 0 sub . sub 8 quantum well were measured at T = 0.335-10 K with varying current between 100 nA and 50 mA. It was found that in high magnetic fields there occurred Shubnikov-de-Haas oscillations, while in weak fields (H<= kOe) a positive magnetoresistance transforming than in a negative one was observed. This peculiarity is due to the effects of weak localization of 2D charge carriers with very close spin-orbit and inelastic scattering time,tau sub s sub o and tau subphi, respectively. This suggests that the spin states are splitted in response to the perturbing potential associated with the generation of a two-dimensional potential well (Rashba mechanism). The analysis of the effects of weak localization yields the characteristic relaxation time...

  20. 2D materials for nanophotonic devices

    Science.gov (United States)

    Xu, Renjing; Yang, Jiong; Zhang, Shuang; Pei, Jiajie; Lu, Yuerui

    2015-12-01

    Two-dimensional (2D) materials have become very important building blocks for electronic, photonic, and phononic devices. The 2D material family has four key members, including the metallic graphene, transition metal dichalcogenide (TMD) layered semiconductors, semiconducting black phosphorous, and the insulating h-BN. Owing to the strong quantum confinements and defect-free surfaces, these atomically thin layers have offered us perfect platforms to investigate the interactions among photons, electrons and phonons. The unique interactions in these 2D materials are very important for both scientific research and application engineering. In this talk, I would like to briefly summarize and highlight the key findings, opportunities and challenges in this field. Next, I will introduce/highlight our recent achievements. We demonstrated atomically thin micro-lens and gratings using 2D MoS2, which is the thinnest optical component around the world. These devices are based on our discovery that the elastic light-matter interactions in highindex 2D materials is very strong. Also, I would like to introduce a new two-dimensional material phosphorene. Phosphorene has strongly anisotropic optical response, which creates 1D excitons in a 2D system. The strong confinement in phosphorene also enables the ultra-high trion (charged exciton) binding energies, which have been successfully measured in our experiments. Finally, I will briefly talk about the potential applications of 2D materials in energy harvesting.

  1. Phase diagram of electronic systems with quadratic Fermi nodes in 2 <d <4 : 2 +ɛ expansion, 4 -ɛ expansion, and functional renormalization group

    Science.gov (United States)

    Janssen, Lukas; Herbut, Igor F.

    2017-02-01

    Several materials in the regime of strong spin-orbit interaction such as HgTe, the pyrochlore iridate Pr2Ir2O7 , and the half-Heusler compound LaPtBi, as well as various systems related to these three prototype materials, are believed to host a quadratic band touching point at the Fermi level. Recently, it has been proposed that such a three-dimensional gapless state is unstable to a Mott-insulating ground state at low temperatures when the number of band touching points N at the Fermi level is smaller than a certain critical number Nc. We further substantiate and quantify this scenario by various approaches. Using ɛ expansion near two spatial dimensions, we show that Nc=64 /(25 ɛ2) +O (1 /ɛ ) and demonstrate that the instability for N 2 <d <4 . Directly in d =3 we therewith find Nc=1.86 , and thus again above the physical N =1 . All these results are consistent with the prediction that the interacting ground state of pure, unstrained HgTe, and possibly also Pr2Ir2O7 , is a strong topological insulator with a dynamically generated gap—a topological Mott insulator.

  2. 2D transition metal dichalcogenides

    Science.gov (United States)

    Manzeli, Sajedeh; Ovchinnikov, Dmitry; Pasquier, Diego; Yazyev, Oleg V.; Kis, Andras

    2017-08-01

    Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of atomic-scale thickness, direct bandgap, strong spin-orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examined and their properties are discussed, with particular attention to their charge density wave, superconductive and topological phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties.

  3. Contrasting 1D tunnel-structured and 2D layered polymorphs of V2O5: relating crystal structure and bonding to band gaps and electronic structure.

    Science.gov (United States)

    Tolhurst, Thomas M; Leedahl, Brett; Andrews, Justin L; Marley, Peter M; Banerjee, Sarbajit; Moewes, Alexander

    2016-06-21

    New V2O5 polymorphs have risen to prominence as a result of their open framework structures, cation intercalation properties, tunable electronic structures, and wide range of applications. The application of these materials and the design of new, useful polymorphs requires understanding their defining structure-property relationships. We present a characterization of the band gap and electronic structure of nanowires of the novel ζ-phase and the orthorhombic α-phase of V2O5 using X-ray spectroscopy and density functional theory calculations. The band gap is found to decrease from 1.90 ± 0.20 eV in the α-phase to 1.50 ± 0.20 eV in the ζ-phase, accompanied by the loss of the α-phase's characteristic split-off dxy band in the ζ-phase. States of dxy origin continue to dominate the conduction band edge in the new polymorph but the inequivalence of the vanadium atoms and the increased local symmetry of [VO6] octahedra results in these states overlapping with the rest of the V 3d conduction band. ζ-V2O5 exhibits anisotropic conductivity along the b direction, defining a 1D tunnel, in contrast to α-V2O5 where the anisotropic conductivity is along the ab layers. We explain the structural origins of the differences in electronic properties that exist between the α- and ζ-phase.

  4. Interlayer couplings, Moiré patterns, and 2D electronic superlattices in MoS2/WSe2 hetero-bilayers

    Science.gov (United States)

    Zhang, Chendong; Chuu, Chih-Piao; Ren, Xibiao; Li, Ming-Yang; Li, Lain-Jong; Jin, Chuanhong; Chou, Mei-Yin; Shih, Chih-Kang

    2017-01-01

    By using direct growth, we create a rotationally aligned MoS2/WSe2 hetero-bilayer as a designer van der Waals heterostructure. With rotational alignment, the lattice mismatch leads to a periodic variation of atomic registry between individual van der Waals layers, exhibiting a Moiré pattern with a well-defined periodicity. By combining scanning tunneling microscopy/spectroscopy, transmission electron microscopy, and first-principles calculations, we investigate interlayer coupling as a function of atomic registry. We quantitatively determine the influence of interlayer coupling on the electronic structure of the hetero-bilayer at different critical points. We show that the direct gap semiconductor concept is retained in the bilayer although the valence and conduction band edges are located at different layers. We further show that the local bandgap is periodically modulated in the X-Y direction with an amplitude of ~0.15 eV, leading to the formation of a two-dimensional electronic superlattice. PMID:28070558

  5. Interlayer couplings, Moiré patterns, and 2D electronic superlattices in MoS 2 /WSe 2 hetero-bilayers

    KAUST Repository

    Zhang, Chendong

    2017-01-07

    By using direct growth, we create a rotationally aligned MoS2/WSe2 hetero-bilayer as a designer van der Waals heterostructure. With rotational alignment, the lattice mismatch leads to a periodic variation of atomic registry between individual van der Waals layers, exhibiting a Moiré pattern with a well-defined periodicity. By combining scanning tunneling microscopy/spectroscopy, transmission electron microscopy, and first-principles calculations, we investigate interlayer coupling as a function of atomic registry. We quantitatively determine the influence of interlayer coupling on the electronic structure of the hetero-bilayer at different critical points. We show that the direct gap semiconductor concept is retained in the bilayer although the valence and conduction band edges are located at different layers. We further show that the local bandgap is periodically modulated in the X-Y direction with an amplitude of ~0.15 eV, leading to the formation of a two-dimensional electronic superlattice.

  6. 二维码电子凭证在移动商务中的应用研究%Study for Application of 2-D Barcode Electronic Bill in Mobile Business

    Institute of Scientific and Technical Information of China (English)

    赵勇军

    2015-01-01

    电子商务是一种新型的商务模式,在目前的市场当中,已经取得了十分广泛的应用。随着移动通信技术和无线网络技术的发展和应用,电子商务正在逐渐朝着移动商务的方向发展。在当前的移动商务领域当中,二维码的应用正在受到越来越多人的重视和关注。本文结合二维码的基本概念和特点,对二维码电子凭证在移动商务中的应用进行了研究。%E-Business is a new type of business mode. It has been widely used in current market. Along with the devel-opment and application of mobile technologies and wireless network technologies,E-business is developing towards the mobile business gradually. In current mobile business industry,2-D barcode is much concerned by more and more peo-ple. Considering the basic concept and characters of 2D-barcode,this article studies the application of 2-D barcode e-lectronic bill in mobile business.

  7. CYP2D6 pharmacogenomics

    Directory of Open Access Journals (Sweden)

    Mohanan Geetha Gopisankar

    2017-10-01

    Full Text Available Cytochromes are proteins that catalyze electron transfer reactions of many metabolic pathways. They are involved in drug metabolism and thus determines the therapeutic safety and efficacy of drugs in patients. Cytochrome P450 in mitochondria accounts for 90% of the oxidative metabolism of clinically used drugs during phase 1 reaction. CYP2D6 is a major gene member of this superfamily as it carries out metabolism of 25% of drugs currently available in the market. Contrary to the concept of specificity of enzyme action these can metabolize substrates of different chemistry. Since its discovery, many have intensively studied this unique hemoprotein and contributed to the elucidation of its molecular properties and physiological functions and also the structure-activity relationships of its substrates and inhibitors. Its activity ranges considerably within a population due to genetic polymorphisms which lead to varied responses to drug intake. Studying such polymorphisms which cause a significant impact in the management of patients and helps to achieve the final target of personalizing medicine. This review briefs about history, structure, and function, molecular genetics, substrates, regulators and inhibitors of CYP2D6 and its clinical pharmacogenomics.

  8. Tuning the conductivity threshold and carrier density of two-dimensional electron gas at oxide interfaces through interface engineering

    Directory of Open Access Journals (Sweden)

    H. J. Harsan Ma

    2015-08-01

    Full Text Available The two-dimensional electron gas (2DEG formed at the perovskite oxides heterostructures is of great interest because of its potential applications in oxides electronics and nanoscale multifunctional devices. A canonical example is the 2DEG at the interface between a polar oxide LaAlO3 (LAO and non-polar SrTiO3 (STO. Here, the LAO polar oxide can be regarded as the modulating or doping layer and is expected to define the electronic properties of 2DEG at the LAO/STO interface. However, to practically implement the 2DEG in electronics and device design, desired properties such as tunable 2D carrier density are necessary. Here, we report the tuning of conductivity threshold, carrier density and electronic properties of 2DEG in LAO/STO heterostructures by insertion of a La0.5Sr0.5TiO3 (LSTO layer of varying thicknesses, and thus modulating the amount of polarization of the oxide over layers. Our experimental result shows an enhancement of carrier density up to a value of about five times higher than that observed at the LAO/STO interface. A complete thickness dependent metal-insulator phase diagram is obtained by varying the thickness of LAO and LSTO providing an estimate for the critical thickness needed for the metallic phase. The observations are discussed in terms of electronic reconstruction induced by polar oxides.

  9. In situ analysis of gas composition by electron energy-loss spectroscopy for environmental transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Crozier, Peter A., E-mail: crozier@asu.edu [School for Engineering of Matter, Transport and Energy, Arizona State University Tempe, AZ 85287-6106 (United States); Chenna, Santhosh [School for Engineering of Matter, Transport and Energy, Arizona State University Tempe, AZ 85287-6106 (United States)

    2011-02-15

    We have developed methods for using in situ electron energy-loss spectroscopy (EELS) to perform quantitative analysis of gas in an environmental transmission electron microscope. Inner-shell EELS was able to successfully determine the composition of gas mixtures with an accuracy of about 15% or better provided that some precautions are taken during the acquisition to account for the extended gas path lengths associated with the reaction cell. The unique valence-loss spectrum associated with many gases allowed simple methodologies to be developed to determine gas composition from the low-loss region of the spectrum from a gas mixture. The advantage of the valence loss approach is that it allows hydrogen to be detected and quantified. EELS allows real-time analysis of the volume of gas inside the reaction cell and can be performed rapidly with typical acquisition times of a few seconds or less. This in situ gas analysis can also be useful for revealing mass transport issues associated with the differential gas diffusion through the system. -- Research Highlights: {yields} In situ electron energy-loss spectroscopy for gas analysis in ETEM. {yields} Compositional accuracy of about 15% or better. {yields} Can use core-loss or valence loss spectroscopy. {yields} Can detect mass transport property of gas handling system.

  10. Friction behaviour of TiAlN films around cubic/hexagonal transition: A 2D grazing incidence X-ray diffraction and electron energy loss spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Pinot, Y. [Université de Haute Alsace, Laboratoire Physique et Mécanique Textiles (EA 4365), F-68093 Mulhouse (France); Pac, M.-J., E-mail: marie-jose.pac@uha.fr [Université de Haute Alsace, Laboratoire Physique et Mécanique Textiles (EA 4365), F-68093 Mulhouse (France); Henry, P. [Université de Haute Alsace, Laboratoire Physique et Mécanique Textiles (EA 4365), F-68093 Mulhouse (France); Rousselot, C. [Université de Franche-Comté, FEMTO-ST (UMR CNRS 6174), F-25211 Montbéliard (France); Odarchenko, Ya.I.; Ivanov, D.A. [Université de Haute Alsace, Institut de Science des Matériaux de Mulhouse (UMR 7361 CNRS), F-68093 Mulhouse (France); Ulhaq-Bouillet, C.; Ersen, O. [Université de Strasbourg, Institut de Physique et Chimie des Matériaux de Strasbourg (UMR CNRS 7504), F-67087 Strasbourg (France); Tuilier, M.-H. [Université de Haute Alsace, Laboratoire Physique et Mécanique Textiles (EA 4365), F-68093 Mulhouse (France)

    2015-02-27

    The properties at different scales of Ti{sub 1−x}Al{sub x}N films deposited by reactive magnetron sputtering from TiAl sintered (S) targets produced by powder metallurgy are compared with those of a set of films previously deposited in the same conditions from mosaic targets (M) made of pure Ti and Al metals. For compositions close to the hcp/fcc transition (around x = 0.6), the friction behaviour, growth directions and organization of crystallized domains are found to be sensitive to the type of target used. The resistance to crack creation is higher for Ti{sub 0.54}Al{sub 0.46}N (S) and Ti{sub 0.38}Al{sub 0.62}N (S) than for Ti{sub 0.50}Al{sub 0.50}N (M) and Ti{sub 0.32}Al{sub 0.68}N (M). From the measurement of mechanical properties, toughness, and wear volumes and from the observation of wear tracks, it is found that films prepared from sintered targets exhibit a better wear resistance. Grazing incidence X-ray diffraction and electron energy loss spectroscopy in Transmission Electronic Microscopy are used to investigate the long- and short-range orders within the films. The morphology of Ti{sub 0.54}Al{sub 0.46}N (S) film can be considered as an array of crystalline domains having reciprocal-space vectors 111 and 200 directed along the meridian but with random in-plane orientation. Ti{sub 0.38}Al{sub 0.62}N (S) Al-rich film presents a random orientation of the crystalline domains whereas Ti{sub 0.32}Al{sub 0.68}N (M) deposited from composite targets exhibits a well-oriented fibrillar structure. The N K-edge Electron Energy Loss Near Edge Spectra are discussed with previous results of Extended X-ray Absorption Fine Structure Spectroscopy, which has evidenced different values of Al–N and Ti–N bond lengths, either octahedral (cubic-like) or tetrahedral (hexagonal-like) within Ti{sub 0.50}Al{sub 0.50}N (M) and Ti{sub 0.32}Al{sub 0.68}N (M) films. For similar compositions, films deposited from sintered alloys contain more nitrogen atoms in octahedral cubic

  11. Chemical Sensing of 2D Graphene/MoS2 Heterostructure device.

    Science.gov (United States)

    Cho, Byungjin; Yoon, Jongwon; Lim, Sung Kwan; Kim, Ah Ra; Kim, Dong-Ho; Park, Sung-Gyu; Kwon, Jung-Dae; Lee, Young-Joo; Lee, Kyu-Hwan; Lee, Byoung Hun; Ko, Heung Cho; Hahm, Myung Gwan

    2015-08-05

    We report the production of a two-dimensional (2D) heterostructured gas sensor. The gas-sensing characteristics of exfoliated molybdenum disulfide (MoS2) connected to interdigitated metal electrodes were investigated. The MoS2 flake-based sensor detected a NO2 concentration as low as 1.2 ppm and exhibited excellent gas-sensing stability. Instead of metal electrodes, patterned graphene was used for charge collection in the MoS2-based sensing devices. An equation based on variable resistance terms was used to describe the sensing mechanism of the graphene/MoS2 device. Furthermore, the gas response characteristics of the heterostructured device on a flexible substrate were retained without serious performance degradation, even under mechanical deformation. This novel sensing structure based on a 2D heterostructure promises to provide a simple route to an essential sensing platform for wearable electronics.

  12. Dimmable Electronic Ballast for a Gas Discharge Lamp

    Science.gov (United States)

    Raducanu, Marius; Hennings, Brian D.

    2013-01-01

    Titanium dioxide (TiO2) is the most efficient photocatalyst for organic oxidative degradation. TiO2 is effective not only in aqueous solution, but also in nonaqueous solvents and in the gas phase. It is photostable, biologically and chemically inert, and non-toxic. Low-energy UV light (approximately 375 nm, UV-A) can be used to photoactivate TiO2. TiO2 photocatalysis has been used to mineralize most types of organic compounds. Also, TiO2 photocatalysis has been effectively used in sterilization. This effectiveness has been demonstrated by its aggressive destruction of microorganisms, and aggressive oxidation effects of toxins. It also has been used for the oxidation of carbon monoxide to carbon dioxide, and ammonia to nitrogen. Despite having many attractive features, advanced photocatalytic oxidation processes have not been effectively used for air cleaning. One of the limitations of the traditional photocatalytic systems is the ballast that powers (lights) the bulbs. Almost all commercial off-the-shelf (COTS) ballasts are not dimmable and do not contain safety features. COTS ballasts light the UV lamp as bright as the bulb can be lit, and this results in shorter bulb lifetime and maximal power consumption. COTS magnetic ballasts are bulky, heavy, and inefficient. Several iterations of dimmable electronic ballasts have been developed. Some manifestations have safety features such as broken-bulb or over-temperature warnings, replace-bulb alert, logbulb operational hours, etc. Several electronic ballast boards capable of independently lighting and controlling (dimming) four fluorescent (UV light) bulbs were designed, fabricated, and tested. Because of the variation in the market bulb parameters, the ballast boards were designed with a very broad range output. The ballast boards can measure and control the current (power) for each channel.

  13. Activated sludge model No. 2d, ASM2d

    DEFF Research Database (Denmark)

    Henze, M.

    1999-01-01

    The Activated Sludge Model No. 2d (ASM2d) presents a model for biological phosphorus removal with simultaneous nitrification-denitrification in activated sludge systems. ASM2d is based on ASM2 and is expanded to include the denitrifying activity of the phosphorus accumulating organisms (PAOs...

  14. Static characterization of bump-type gas foil bearing: intergration of top foil 2-D thick plate model%基于二维厚板模型的波箔片轴承静特性

    Institute of Scientific and Technical Information of China (English)

    刘占生; 徐方程; 张广辉; 曹智选

    2012-01-01

    The 2-D (two-dimensional) thick plate finite element model for top foil was developed. By using coupled finite element mothod and finite difference method, the com- pressible gas lubricated Reynolds equation and the film thickness equation were solved cou- pling together. Predictions of minimum gas film thickness for increasing static loads at two speeds were obtained for bearing mid-plane and edge of bump-type gas foil bearing. The nu- merical results of this finite element model were compared with 1-D (one-dimensional) beam model model, 2-D shin shell model and test data. The results indicate that the minimum film thickness of three models agree well with test data at bearing min-plane, but at bearing edge, the accuracy of 2-D thick plate model is the highest due to its shear effect. 1-D beam model can not reflect film thickness variation along the bearing length direction because it on- ly considers the circumferential direction. The study in this paper established the theoretical foundation of dynamic characteristics research of bump-type gas foil bearing.%建立平箔片的二维厚板有限元模型,运用有限单元法和有限差分法耦合求解Reynolds方程和气膜厚度方程,研究了在两个工作转速下气体波箔片轴承在中截面和边缘处最小气膜厚度随轴承承载力变化规律.通过数值仿真对该模型、一维梁模型、二维薄壳模型和文献实验数据进行对比分析,结果表明:在轴承中截面处,3个模型的最小气膜厚度仿真结果都与实验结果符合得很好,但在轴承边缘处,由于二维厚板模型考虑了平箔片的剪切效应,因此其最小气膜厚度比二维薄壳模型的结果更接近实验值,而一维梁模型只考虑轴承圆周方向,因此不能体现气膜厚度沿轴承长度方向的变化规律.通过研究,为分析箔片轴承动力学特性奠定了理论基础.

  15. A new integrated photosensor for gas proportional scintillation counters based on the gas electron multiplier (GEM)

    CERN Document Server

    Lopes, J A M; Conde, C A N; Morgado, R E

    1999-01-01

    The performance of a novel integrated photosensor for use in a xenon gas proportional scintillation detector is described. Earlier integrated photo-sensor designs were limited in charge gains due to the onset of electrical breakdown, which was ascribed to optical positive feedback from scintillation photons produced in the charge amplification stage. The present design uses a gas electron multiplier (GEM) composed of a 50 mu m thick Kapton film with copper-plated electrode surfaces on both sides and perforated with 200 mu m holes at a 300 mu m pitch. The front surface is made photosensitive with a 150-nm-thick CsI film. When an appropriate voltage is applied between the copper electrodes, the resulting electric field directs photoelectrons produced on the front surface through the holes in the GEM and onto a wire chamber where charge amplification occurs. Optical positive feedback is essentially eliminated since the charge amplification stage is optically de-coupled from the photocathode. The GEM also provide...

  16. Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

    Energy Technology Data Exchange (ETDEWEB)

    Maiuri, Margherita [CNR-IFN, Dipartimento di Fisica, Politecnico di Milano, P.zza L. da Vinci 32, Milano 20133 (Italy); Department of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544 (United States); Réhault, Julien; Polli, Dario; Cerullo, Giulio, E-mail: giulio.cerullo@polimi.it [CNR-IFN, Dipartimento di Fisica, Politecnico di Milano, P.zza L. da Vinci 32, Milano 20133 (Italy); Carey, Anne-Marie; Hacking, Kirsty; Cogdell, Richard J. [Glasgow Biomedical Research Centre, IBLS, University of Glasgow, 126 Place, Glasgow G12 8TA, Scotland (United Kingdom); Garavelli, Marco [Dipartimento di Chimica “G. Ciamician,” Università di Bologna, Via Selmi 2, IT-40126 Bologna (Italy); CNRS, Institut de Chimie de Lyon, École Normale Supérieure de Lyon, Université de Lyon, 46 Allée d’Italie, F-69364 Lyon Cedex 07 (France); Lüer, Larry [Madrid Institute for Advanced Studies, IMDEA Nanociencia, Madrid (Spain)

    2015-06-07

    We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Q{sub x} and Q{sub y} transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S{sub 2} of the Spx towards the Q{sub x} state of the B890, and (iii) the internal conversion from Q{sub x} to Q{sub y} within the B890.

  17. Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

    Science.gov (United States)

    Maiuri, Margherita; Réhault, Julien; Carey, Anne-Marie; Hacking, Kirsty; Garavelli, Marco; Lüer, Larry; Polli, Dario; Cogdell, Richard J.; Cerullo, Giulio

    2015-06-01

    We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Qx and Qy transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S2 of the Spx towards the Qx state of the B890, and (iii) the internal conversion from Qx to Qy within the B890.

  18. Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium.

    Science.gov (United States)

    Maiuri, Margherita; Réhault, Julien; Carey, Anne-Marie; Hacking, Kirsty; Garavelli, Marco; Lüer, Larry; Polli, Dario; Cogdell, Richard J; Cerullo, Giulio

    2015-06-01

    We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Qx and Qy transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S2 of the Spx towards the Qx state of the B890, and (iii) the internal conversion from Qx to Qy within the B890.

  19. Collective electronic excitations in the ultra violet regime in 2-D and 1-D carbon nanostructures achieved by the addition of foreign atoms

    Science.gov (United States)

    Bangert, U.; Pierce, W.; Boothroyd, C.; Pan, C.-T.; Gwilliam, R.

    2016-06-01

    Plasmons in the visible/UV energy regime have attracted great attention, especially in nano-materials, with regards to applications in opto-electronics and light harvesting; tailored enhancement of such plasmons is of particular interest for prospects in nano-plasmonics. This work demonstrates that it is possible, by adequate doping, to create excitations in the visible/UV regime in nano-carbon materials, i.e., carbon nanotubes and graphene, with choice of suitable ad-atoms and dopants, which are introduced directly into the lattice by low energy ion implantation or added via deposition by evaporation. Investigations as to whether these excitations are of collective nature, i.e., have plasmonic character, are carried out via DFT calculations and experiment-based extraction of the dielectric function. They give evidence of collective excitation behaviour for a number of the introduced impurity species, including K, Ag, B, N, and Pd. It is furthermore demonstrated that such excitations can be concentrated at nano-features, e.g., along nano-holes in graphene through metal atoms adhering to the edges of these holes.

  20. Current-injection in a ballastic multiterminal superconductor/two-dimensional electron gas Josephson junction

    NARCIS (Netherlands)

    Schäpers, Th.; Guzenko, V.A.; Müller, R.P.; Golubov, A.A.; Brinkman, A.; Crecelius, G.; Kaluza, A.; Lüth, H.

    2003-01-01

    We study the suppression of the critical current in a multi-terminal superconductor/two-dimensional electron gas/superconductor Josephson junction by means of hot carrier injection. As a superconductor Nb is used, while the two-dimensional electron gas is located in a strained InGaAs/InP heterostruc

  1. Determination of phosphine and other fumigants in air samples by thermal desorption and 2D heart-cutting gas chromatography with synchronous SIM/Scan mass spectrometry and flame photometric detection.

    Science.gov (United States)

    Fahrenholtz, Svea; Hühnerfuss, Heinrich; Baur, Xaver; Budnik, Lygia Therese

    2010-12-24

    Fumigants and volatile industrial chemicals are particularly hazardous to health when a freight container is fumigated or the contaminated material is introduced into its enclosed environment. Phosphine is now increasingly used as a fumigant, after bromomethane--the former fumigant of choice--has been banned by the Montreal Protocol. We have enhanced our previously established thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method by integrating a second gas chromatographic dimension and a flame photometric detector to allow the simultaneous detection of phosphine and volatile organic compounds (VOCs), providing a novel application. A thermal desorption system is coupled to a two dimensional gas chromatograph using both mass spectrometric and flame photometric detection (TD-2D-GC-MS/FPD). Additionally, the collection of mass spectrometric SIM and Scan data has been synchronised, so only a single analysis is now sufficient for qualitative scanning of the whole sample and for sensitive quantification. Though detection limits for the herewith described method are slightly higher than in the previous method, they are in the low μL m(-3) range, which is not only below the respective occupational exposure and intervention limits but also allows the detection of residual contamination after ventilation. The method was developed for the separation and identification of 44 volatile substances. For 12 of these compounds (bromomethane, iodomethane, dichloromethane, 1,2-dichlorethane, benzene, tetrachloromethane, 1,2-dichloropropane, toluene, trichloronitromethane, ethyl benzene, phosphine, carbon disulfide) the method was validated as we chose the target compounds due to their relevance in freight container handling.

  2. Influence of gas pressure on electron beam emission current of pulsed cathodic-arc-based forevacuum plasma electron source

    Science.gov (United States)

    Burdovitsin, Victor A.; Kazakov, Andrey V.; Medovnik, Alexander V.; Oks, Efim M.

    2017-09-01

    We describe our experimental investigation of the effect of background gas pressure on the emission parameters of a pulsed cathodic-arc-based forevacuum-pressure plasma-cathode electron source. We find that increased gas pressure over the range 4-16 Pa significantly reduces the beam current rise-time and significantly increases the emission current amplitude. For example, at a discharge current of 20 A, increasing the working gas pressure from 4 Pa to 16 Pa increases the emission current from 8 A to 18 A and shortens the beam rise-time from 50 μs to 20 μs. This influence of gas pressure on the electron beam parameters can be explained by the effect of arc discharge current switching from the anode to emission. In our case, the current switching effect is caused by increased working gas pressure. In the forevacuum pressure range, the increase of the electron emission current with the growth of gas pressure is due to a rise in the emission plasma potential which is caused by ion back-streaming from the plasma formed in the electron beam transport region. A model describing the influence of gas pressure on the electron emission from the plasma is presented.

  3. Quantum magnetotransport in a modulated two-dimensional electron gas

    Science.gov (United States)

    Park, Tae-ik; Gumbs, Godfrey

    1997-09-01

    Quantum mechanical calculations of the magnetotransport coefficients of a modulated two-dimensional electron gas in a perpendicular magnetic field are presented using the Kubo method. The model modulation potential used is such that the effect of the steepness of the potential and its strength on the band part of the longitudinal resistivity ρxxand the Hall resistivity ρxycould be studied. In the extreme limit of a very steep potential, a two-dimensional square array of antidots is simulated. Impurity scattering is included in the self-consistent t-matrix approximation. The results show that for a strong lateral superlattice potential, ρxyis quenched in the low magnetic field regime and as the magnetic field increases there is a large negative Hall resistivity. The intensity of this negative peak is suppressed as the strength of the modulation potential is decreased. It is also shown that the height of the negative peak depends on the steepness of the potential. The longitudinal resistivity also has some interesting features. There are Aharonov-Bohm oscillations and a double peak structure which depends on both the strength of the modulation potential as well as its slope. The numerical results show that the position and intensity of the lower peak is not very sensitive to a change in the strength of the lattice potential or its steepness. However, the upper peak is greatly reduced when the lattice potential is diminished in strength. The double peak feature in ρxxand the negative peak and quenching of the Hall effect at low magnetic fields have been observed experimentally for antidots in both the quasiclassical and quantum regimes.

  4. Ultrafast electronic relaxation of excited state vitamin B{sub 12} in the gas phase

    Energy Technology Data Exchange (ETDEWEB)

    Shafizadeh, Niloufar [Laboratoire de Photophysique Moleculaire, U.P.R. 3361 CNRS Bat 210, Universite de Paris-Sud, 91405 Orsay, Cedex (France)], E-mail: Niloufar.Shafizadeh@u-psud.fr; Poisson, Lionel; Soep, Benoit [Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM - CNRS URA 2453, CEA Saclay, 91191 Gif-sur-Yvette Cedex (France)

    2008-06-23

    The time evolution of electronically excited vitamin B{sub 12} (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  5. Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase

    Science.gov (United States)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  6. Stationary afterglow measurements of the temperature dependence of the electron–ion recombination rate coefficients of {{\\rm{H}}}_{2}{{\\rm{D}}}^{+} and {{HD}}_{2}^{+} in He/Ar/H2/D2 gas mixtures at T = 80–145 K 

    Science.gov (United States)

    Plašil, Radek; Dohnal, Petr; Kálosi, Ábel; Roučka, Štěpán; Johnsen, Rainer; Glosík, Juraj

    2017-03-01

    We report measurements of the binary and ternary recombination rate coefficients of deuterated isotopologues of {{{H}}}3+. A cavity ring-down absorption spectrometer was used to monitor the fractional abundances of {{{H}}}3+, {{{H}}}2{{{D}}}+, {{HD}}2+ and {{{D}}}3+ during the decay of a plasma in He/Ar/{{{H}}}2/{{{D}}}2 mixtures. A dependence of the measured effective recombination rate coefficients on the helium buffer gas density was observed and hence both the binary and the ternary recombination rate coefficients for {{{H}}}2{{{D}}}+ and {{HD}}2+ were obtained in the temperature range 80–145 K.

  7. Exact e-e (exchange) correlations of 2-D quantum dots in magnetic field: Size extensive N = 3 , 4 , … , ‧ n ‧ -electron systems via multi-pole expansion

    Science.gov (United States)

    Aggarwal, Priyanka; Sharma, Shivalika; Singh, Sunny; Kaur, Harsimran; Hazra, Ram Kuntal

    2017-04-01

    Inclusion of coulomb interaction emerges with the complexity of either convergence of integrals or separation of variables of Schrödinger equations. For an N-electron system, interaction terms grow by N(N-1)/2 factors. Therefore, 2-e system stands as fundamental basic unit for generalized N-e systems. For the first time, we have evaluated e-e correlations in very simple and absolutely terminating finite summed hypergeometric series for 2-D double carrier parabolic quantum dot in both zero and arbitrary non-zero magnetic field (symmetric gauge) and have appraised these integrals in variational methods. The competitive role among confinement strength, magnetic field, mass of the carrier and dielectric constant of the medium on energy level diagram, level-spacing statistics, heat capacities (Cv at 1 K) and magnetization (T ∼ (0-1)K) is studied on systems spanning over wide range of materials (GaAs,Ge,CdS,SiO2 and He, etc). We have also constructed an exact theory for generalized correlated N-e 2-D quantum dots via multi-pole expansion but for the sake of compactness of the article we refrain from data.

  8. Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

    Science.gov (United States)

    Grishkov, A. A.; Kornilov, S. Yu.; Rempe, N. G.; Shidlovskiy, S. V.; Shklyaev, V. A.

    2016-07-01

    The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

  9. Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

    Energy Technology Data Exchange (ETDEWEB)

    Grishkov, A. A. [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation); Kornilov, S. Yu., E-mail: kornilovsy@gmail.com; Rempe, N. G. [Tomsk State University of Control Systems and Radioelectronics (Russian Federation); Shidlovskiy, S. V. [Tomsk State University (Russian Federation); Shklyaev, V. A. [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)

    2016-07-15

    The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

  10. Completing electron scattering studies with the inert gas column:e - Rn scattering and Ionization

    CERN Document Server

    Joshi, Foram M; Chaudhari, Asha S; Modi, Hitesh S; Pindaria, Manish J

    2016-01-01

    Interest in the inert or noble- gas atoms in general arises because they are ideal as test systems for various theoretical models of electron scattering and also since their interaction processes serve as reference for the determination of instrumental responses in electron scattering experiments. The ionization cross section data of ground state inert gas atoms He through Xe are considered to be benchmark data. Our aim in this paper is to provide theoretical results on electron scattering with Radon atoms, as it would complete the studies on the entire inert gas column. That is possible with this particular column only, in view of the preceding literature on He through Xe . Inert gas radon is radioactive, and would be a difficult target for electron scattering experiments. In the present calculations, the complications arising from radioactivity are not considered. We provide hitherto unavailable cross sections on atomic radon, and also provide opportunity of the comparison of electron impact cross sections ...

  11. Enhanced electron yield from a laser-plasma accelerator using high-Z gas jet targets

    CERN Document Server

    Mirzaie, Mohammad; Li, Song; Sokollik, Thomas; He, Fei; Cheng, Ya; Sheng, Zhengming; Zhang, Jie

    2014-01-01

    An investigation of the multi-hundred MeV electron beam yield (charge) form helium, nitrogen, neon and argon gas jet plasmas in a laser-plasma wakefield acceleration experiment was carried out. The charge measurement has been made via imaging the electron beam intensity profile on a fluorescent screen into a 14-bit charge coupled device (CCD) which was cross-calibrated with nondestructive electronics-based method. Within given laser and plasma parameters, we found that laser-driven low Z- gas jet targets generate high-quality and well-collimated electron beams with reasonable yields at the level of 10-100 pC. On the other hand, filamentary electron beams which were observed from high-Z gas jets at higher densities reached much higher yield. Evidences for cluster formation were clearly observed in high-Z gases, especially in the argon gas jet target where we received the highest yield of ~ 3 nC

  12. Quasiparticle interference in unconventional 2D systems

    Science.gov (United States)

    Chen, Lan; Cheng, Peng; Wu, Kehui

    2017-03-01

    At present, research of 2D systems mainly focuses on two kinds of materials: graphene-like materials and transition-metal dichalcogenides (TMDs). Both of them host unconventional 2D electronic properties: pseudospin and the associated chirality of electrons in graphene-like materials, and spin-valley-coupled electronic structures in the TMDs. These exotic electronic properties have attracted tremendous interest for possible applications in nanodevices in the future. Investigation on the quasiparticle interference (QPI) in 2D systems is an effective way to uncover these properties. In this review, we will begin with a brief introduction to 2D systems, including their atomic structures and electronic bands. Then, we will discuss the formation of Friedel oscillation due to QPI in constant energy contours of electron bands, and show the basic concept of Fourier-transform scanning tunneling microscopy/spectroscopy (FT-STM/STS), which can resolve Friedel oscillation patterns in real space and consequently obtain the QPI patterns in reciprocal space. In the next two parts, we will summarize some pivotal results in the investigation of QPI in graphene and silicene, in which systems the low-energy quasiparticles are described by the massless Dirac equation. The FT-STM experiments show there are two different interference channels (intervalley and intravalley scattering) and backscattering suppression, which associate with the Dirac cones and the chirality of quasiparticles. The monolayer and bilayer graphene on different substrates (SiC and metal surfaces), and the monolayer and multilayer silicene on a Ag(1 1 1) surface will be addressed. The fifth part will introduce the FT-STM research on QPI in TMDs (monolayer and bilayer of WSe2), which allow us to infer the spin texture of both conduction and valence bands, and present spin-valley coupling by tracking allowed and forbidden scattering channels.

  13. Orthotropic Piezoelectricity in 2D Nanocellulose

    Science.gov (United States)

    García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.

    2016-10-01

    The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V‑1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.

  14. Operation of gas electron multiplier (GEM) with propane gas at low pressure and comparison with tissue-equivalent gas mixtures

    Energy Technology Data Exchange (ETDEWEB)

    De Nardo, L., E-mail: laura.denardo@unipd.it [University of Padova, Physics and Astronomy Department and PD-INFN, via Marzolo 8, I-35131 Padova (Italy); Farahmand, M., E-mail: majid.farahmand@rivm.nl [Centre for Environmental Safety and Security, National Institute for Public Health and the Environment (RIVM), PO Box 1, NL-3720 BA Bilthoven (Netherlands)

    2016-05-21

    A Tissue-Equivalent Proportional Counter (TEPC), based on a single GEM foil of standard geometry, has been tested with pure propane gas at low pressure, in order to simulate a tissue site of about 1 µm equivalent size. In this work, the performance of GEM with propane gas at a pressure of 21 and 28 kPa will be presented. The effective gas gain was measured in various conditions using a {sup 244}Cm alpha source. The dependence of effective gain on the electric field strength along the GEM channel and in the drift and induction region was investigated. A maximum effective gain of about 5×10{sup 3} has been reached. Results obtained in pure propane gas are compared with gas gain measurements in gas mixtures commonly employed in microdosimetry, that is propane and methane based Tissue-Equivalent gas mixtures.

  15. Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology.

    Science.gov (United States)

    Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr

    2016-02-06

    The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.

  16. Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology

    Directory of Open Access Journals (Sweden)

    Kateryna Shavanova

    2016-02-01

    Full Text Available The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical. A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.

  17. Calculation of Gas and Electronic Temperatures in the Channel of the Direct Current Arc

    Science.gov (United States)

    Gerasimov, Alexander V.; Kirpichnikov, Alexander P.

    2009-10-01

    The results of calculations of gas and electronic temperatures in the channel of an arc plasma generator are presented. The calculations were carried out within the framework of a self-consistent two-temperature channel model of an arc discharge. The given method can be used with good precision to determine the radial distribution of gas and electronic temperatures in conducting and non-conducting zones of a constant current arc at designated parameters of the discharge (current intensity and power).

  18. Energy losses of positive and negative charged particles in electron gas

    Science.gov (United States)

    Diachenko, M. M.; Kholodov, R. I.

    2017-02-01

    A heavy charged particle propagation through electron gas has been studied using combination of non-relativistic quantum mechanics and the Green’s functions method. The energy loss of a charged particle has been found in the case of large transferred momentum taking into account the interference term in the expression for the rate. The dependence of the energy loss of a charged particles in electron gas with nonzero temperature on the sign of the charge has been obtained.

  19. Performance of one-body reduced density-matrix functionals for the homogeneous electron gas

    Science.gov (United States)

    Lathiotakis, N. N.; Helbig, N.; Gross, E. K. U.

    2007-05-01

    The subject of this study is the exchange-correlation-energy functional of reduced density-matrix functional theory. Approximations of this functional are tested by applying them to the homogeneous electron gas. We find that two approximations recently proposed by Gritsenko , [J. Chem. Phys. 122, 204102 (2005)] yield considerably better correlation energies and momentum distributions than previously known functionals. We introduce modifications to these functionals, which, by construction, reproduce the exact correlation energy of the homogeneous electron gas.

  20. Electronic Nose Functionality for Breath Gas Analysis during Parabolic Flight

    Science.gov (United States)

    Dolch, Michael E.; Hummel, Thomas; Fetter, Viktor; Helwig, Andreas; Lenic, Joachim; Moukhamedieva, Lana; Tsarkow, Dimitrij; Chouker, Alexander; Schelling, Gustav

    2017-02-01

    The presence of humans in space represents a constant threat for their health and safety. Environmental factors such as living in a closed confinement, as well as exposure to microgravity and radiation, are associated with significant changes in bone metabolism, muscular atrophy, and altered immune response, which has impacts on human performance and possibly results in severe illness. Thus, maintaining and monitoring of crew health status has the highest priority to ensure whole mission success. With manned deep space missions to moon or mars appearing at the horizon where short-term repatriation back to earth is impossible the availability of appropriate diagnostic platforms for crew health status is urgently needed. In response to this need, the present experiment evaluated the functionality and practicability of a metal oxide based sensor system (eNose) together with a newly developed breath gas collecting device under the condition of altering acceleration. Parabolic flights were performed with an Airbus A300 ZeroG at Bordeaux, France. Ambient air and exhaled breath of five healthy volunteers was analyzed during steady state flight and parabolic flight maneuvres. All volunteers completed the study, the breath gas collecting device valves worked appropriately, and breathing through the collecting device was easy and did not induce discomfort. During breath gas measurements, significant changes in metal oxide sensors, mainly sensitive to aromatic and sulphur containing compounds, were observed with alternating conditions of acceleration. Similarly, metal oxide sensors showed significant changes in all sensors during ambient air measurements. The eNose as well as the newly developed breath gas collecting device, showed appropriate functionality and practicability during alternating conditions of acceleration which is a prerequisite for the intended use of the eNose aboard the International Space Station (ISS) for breath gas analysis and crew health status

  1. Electronic Nose Functionality for Breath Gas Analysis during Parabolic Flight

    Science.gov (United States)

    Dolch, Michael E.; Hummel, Thomas; Fetter, Viktor; Helwig, Andreas; Lenic, Joachim; Moukhamedieva, Lana; Tsarkow, Dimitrij; Chouker, Alexander; Schelling, Gustav

    2017-06-01

    The presence of humans in space represents a constant threat for their health and safety. Environmental factors such as living in a closed confinement, as well as exposure to microgravity and radiation, are associated with significant changes in bone metabolism, muscular atrophy, and altered immune response, which has impacts on human performance and possibly results in severe illness. Thus, maintaining and monitoring of crew health status has the highest priority to ensure whole mission success. With manned deep space missions to moon or mars appearing at the horizon where short-term repatriation back to earth is impossible the availability of appropriate diagnostic platforms for crew health status is urgently needed. In response to this need, the present experiment evaluated the functionality and practicability of a metal oxide based sensor system (eNose) together with a newly developed breath gas collecting device under the condition of altering acceleration. Parabolic flights were performed with an Airbus A300 ZeroG at Bordeaux, France. Ambient air and exhaled breath of five healthy volunteers was analyzed during steady state flight and parabolic flight maneuvres. All volunteers completed the study, the breath gas collecting device valves worked appropriately, and breathing through the collecting device was easy and did not induce discomfort. During breath gas measurements, significant changes in metal oxide sensors, mainly sensitive to aromatic and sulphur containing compounds, were observed with alternating conditions of acceleration. Similarly, metal oxide sensors showed significant changes in all sensors during ambient air measurements. The eNose as well as the newly developed breath gas collecting device, showed appropriate functionality and practicability during alternating conditions of acceleration which is a prerequisite for the intended use of the eNose aboard the International Space Station (ISS) for breath gas analysis and crew health status

  2. Electron impact ionization of the gas-phase sorbitol

    Science.gov (United States)

    Chernyshova, Irina; Markush, Pavlo; Zavilopulo, Anatoly; Shpenik, Otto

    2015-03-01

    Ionization and dissociative ionization of the sorbitol molecule by electron impact have been studied using two different experimental methods. In the mass range of m/ z = 10-190, the mass spectra of sorbitol were recorded at the ionizing electron energies of 70 and 30 eV. The ion yield curves for the fragment ions have been analyzed and the appearance energies of these ions have been determined. The relative total ionization cross section of the sorbitol molecule was measured using monoenergetic electron beam. Possible fragmentation pathways for the sorbitol molecule were proposed.

  3. Boltzmann equation for the electron gas of a nondegenerate plasma

    Science.gov (United States)

    Gould, R. J.

    1974-01-01

    The collision terms in the Boltzmann equation associated with various processes are derived. For processes having a Fokker-Planck (F-P) limit, the associated F-P operator is derived by means of physical arguments to determine the form of the operator; its multiplying constant is fixed by calculating the total energy exchange rate and comparing with the rate computed by other means. In this manner, the F-P operator is derived for electron-ion scattering, electron-electron scattering in the high-velocity limit, electron-atom elastic scattering, Compton scattering, and the high-velocity limit for inelastic scattering. Other processes considered are bremsstrahlung, radiative-recombination, photoionization, collisional ionization of atoms, and suprathermal-particle ionization of atoms.

  4. Qualitative analysis of Copaifera oleoresin using comprehensive two-dimensional gas chromatography and gas chromatography with classical and cold electron ionisation mass spectrometry.

    Science.gov (United States)

    Wong, Yong Foo; Uekane, Thais M; Rezende, Claudia M; Bizzo, Humberto R; Marriott, Philip J

    2016-12-16

    Improved separation of both sesquiterpenes and diterpenic acids in Copaifera multijuga Hayne oleoresin, is demonstrated by using comprehensive two-dimensional gas chromatography (GC×GC) coupled to accurate mass time-of-flight mass spectrometry (accTOFMS). GC×GC separation employs polar phases (including ionic liquid phases) as the first dimension ((1)D) column, combined with a lower polarity (2)D phase. Elution temperatures (Te) of diterpenic acids (in methyl ester form, DAME) increased as the (1)D McReynolds' polarity value of the column phase decreased. Since Te of sesquiterpene hydrocarbons decreased with increased polarity, the very polar SLB-IL111 (1)D phase leads to excessive peak broadening in the (2)D apolar phase due to increased second dimension retention ((2)tR). The combination of SLB-IL59 with a nonpolar column phase was selected, providing reasonable separation and low Te for sesquiterpenes and DAME, compared to other tested column sets, without excessive (2)tR. Identities of DAME were aided by both soft (30eV) electron ionisation (EI) accurate mass TOFMS analysis and supersonic molecular beam ionisation (cold EI) TOFMS, both which providing less fragmentation and increased relative abundance of molecular ions. The inter-relation between EI energies, emission current, signal-to-noise and mass error for the accurate mass measurement of DAME are reported. These approaches can be used as a basis for conducting of GC×GC with soft EI accurate mass measurement of terpenes, particularly for unknown phytochemicals.

  5. Schottky diodes from 2D germanane

    Science.gov (United States)

    Sahoo, Nanda Gopal; Esteves, Richard J.; Punetha, Vinay Deep; Pestov, Dmitry; Arachchige, Indika U.; McLeskey, James T.

    2016-07-01

    We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe2 framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.

  6. Schottky diodes from 2D germanane

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, Nanda Gopal; Punetha, Vinay Deep [Nanoscience and Nanotechnology Centre, Department of Chemistry, Kumaun University, Nainital, 263001 Uttarakhand (India); Esteves, Richard J; Arachchige, Indika U. [Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Pestov, Dmitry [Nanomaterials Core Characterization Center, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); McLeskey, James T., E-mail: JamesMcLeskey@rmc.edu [Department of Physics, Randolph-Macon College, Ashland, Virginia 23005 (United States)

    2016-07-11

    We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe{sub 2} framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.

  7. Spin and charge transport in a gated two dimensional electron gas

    NARCIS (Netherlands)

    Lerescu, Alexandru Ionut

    2007-01-01

    The work presented in this thesis is centered around the idea of how one can inject, transport and detect the electron's spin in a two dimensional electron gas (a semiconductor heterostructure). Metal based spintronic devices have been established to be the easy way to implement spintronic concepts

  8. Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts

    DEFF Research Database (Denmark)

    Hu, C.-M.; Nitta, Junsaku; Jensen, Ane

    2001-01-01

    Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spin...

  9. Thermodynamics of Two-Dimensional Electron Gas in a Magnetic Field

    Directory of Open Access Journals (Sweden)

    V. I. Nizhankovskii

    2011-01-01

    Full Text Available Change of the chemical potential of electrons in a GaAs-AlGa1−As heterojunction was measured in magnetic fields up to 6.5 T at several temperatures from 2.17 to 12.3 K. A thermodynamic equation of state of two-dimensional electron gas well describes the experimental results.

  10. Investigation of Vortex Structures in Gas-Discharge Nonneutral Electron Plasma: I. Experimental Technique

    CERN Document Server

    Kervalishvili, N A

    2015-01-01

    The nonperturbing experimental methods have been described, by means of which the solitary vortex structures in gas-discharge nonneutral electron plasma were detected and investigated. The comparison with the experimental methods used in devices with pure electron plasma was made. The problems of shielding the electrostatic perturbations in nonneutral plasmas were considered.

  11. Numerical study of the generation of runaway electrons in a gas diode with a hot channel

    Energy Technology Data Exchange (ETDEWEB)

    Lisenkov, V. V., E-mail: lisenkov@iep.uran.ru [Institute of Electrophysics UrB RAS, 106 Amundsena St., Ekaterinburg 620012 (Russian Federation); Ural Federal University, 19 Mira St., Ekaterinburg 620002 (Russian Federation); Shklyaev, V. A., E-mail: shklyaev@to.hcei.tsc.ru [Institute of High Current Electronics SD RAS, 2/3 Akademichesky Avenue, 634055 Tomsk (Russian Federation); National Research Tomsk Polytechnic University, 30 Lenin Avenue, 634050 Tomsk (Russian Federation)

    2015-11-15

    A new method for increasing the efficiency of runaway electron beam generation in atmospheric pressure gas media has been suggested and theoretically proved. The method consists of creating a hot region (e.g., a spark channel or a laser plume) with a decreased numerical density of gas molecules (N) near the cathode. In this method, the ratio E/N (E—electric field strength) is increased by decreasing N instead of increasing E, as has been done in the past. The numerical model that is used allows the simultaneous calculation of the formation of a subnanosecond gas discharge and the generation of runaway electrons in gas media. The calculations have demonstrated the possibility of obtaining current pulses of runaway electrons with amplitudes of hundred of amperes and durations of more than 100 ps. The influence of the hot channel geometry on the parameters of the generated beam has been investigated.

  12. Fabrication and test of digital output interface devices for gas turbine electronic controls

    Science.gov (United States)

    Newirth, D. M.; Koenig, E. W.

    1978-01-01

    A program was conducted to develop an innovative digital output interface device, a digital effector with optical feedback of the fuel metering valve position, for future electronic controls for gas turbine engines. A digital effector (on-off solenoids driven directly by on-off signals from a digital electronic controller) with optical position feedback was fabricated, coupled with the fuel metering valve, and tested under simulated engine operating conditions. The testing indicated that a digital effector with optical position feedback is a suitable candidate, with proper development for future digital electronic gas turbine controls. The testing also identified several problem areas which would have to be overcome in a final production configuration.

  13. Electron and phonon properties and gas storage in carbon honeycomb

    CERN Document Server

    Gao, Yan; Zhong, Chengyong; Zhang, Zhongwei; Xie, Yuee; Zhang, Shengbai

    2016-01-01

    A new kind of three-dimensional carbon allotropes, termed carbon honeycomb (CHC), has recently been synthesized [PRL 116, 055501 (2016)]. Based on the experimental results, a family of graphene networks are constructed, and their electronic and phonon properties are calculated by using first principles methods. All networks are porous metal with two types of electron transport channels along the honeycomb axis and they are isolated from each other: one type of channels is originated from the orbital interactions of the carbon zigzag chains and is topologically protected, while the other type of channels is from the straight lines of the carbon atoms that link the zigzag chains and is topologically trivial. The velocity of the electrons can reach ~106 m/s. Phonon transport in these allotropes is strongly anisotropic, and the thermal conductivities can be very low when compared with graphite by at least a factor of 15. Our calculations further indicate that these porous carbon networks possess high storage capa...

  14. Electron-gas clusters: the ultimate jellium model

    Science.gov (United States)

    Koskinen, M.; Lipas, P. O.; Manninen, M.

    1995-12-01

    The local spin-density approximation is used to calculate ground- and isomeric-state geometries of jellium clusters with 2 to 22 electrons. The positive background charge of the model is completely deformable, both in shape and in density. The model has no input parameters. The resulting shapes of the clusters exhibit breaking of axial and inversion symmetries; in general the shapes are far from ellipsoidal. Those clusters which lack inversion symmetry are extremely soft against odd-multipole deformations. Some clusters can be interpreted as molecules built from magic clusters. The deformation produces a gap at the Fermi level. This results in a regular odd-even staggering of the total energy per electron and of the HOMO level. The strongly deformed 14-electron cluster is semimagic. Stable isomers are predicted. The splitting of the plasmon resonance due to deformation is estimated on a classical argument.

  15. HypGrid2D. A 2-d mesh generator

    Energy Technology Data Exchange (ETDEWEB)

    Soerensen, N.N.

    1998-03-01

    The implementation of a hyperbolic mesh generation procedure, based on an equation for orthogonality and an equation for the cell face area is described. The method is fast, robust and gives meshes with good smoothness and orthogonality. The procedure is implemented in a program called HypGrid2D. The HypGrid2D program is capable of generating C-, O- and `H`-meshes for use in connection with the EllipSys2D Navier-Stokes solver. To illustrate the capabilities of the program, some test examples are shown. First a series of C-meshes are generated around a NACA-0012 airfoil. Secondly a series of O-meshes are generated around a NACA-65-418 airfoil. Finally `H`-meshes are generated over a Gaussian hill and a linear escarpment. (au)

  16. Electron and phonon properties and gas storage in carbon honeycombs

    Science.gov (United States)

    Gao, Yan; Chen, Yuanping; Zhong, Chengyong; Zhang, Zhongwei; Xie, Yuee; Zhang, Shengbai

    2016-06-01

    A new kind of three-dimensional carbon allotrope, termed carbon honeycomb (CHC), has recently been synthesized [PRL 116, 055501 (2016)]. Based on the experimental results, a family of graphene networks has been constructed, and their electronic and phonon properties are studied by various theoretical approaches. All networks are porous metals with two types of electron transport channels along the honeycomb axis and they are isolated from each other: one type of channel originates from the orbital interactions of the carbon zigzag chains and is topologically protected, while the other type of channel is from the straight lines of the carbon atoms that link the zigzag chains and is topologically trivial. The velocity of the electrons can reach ~106 m s-1. Phonon transport in these allotropes is strongly anisotropic, and the thermal conductivities can be very low when compared with graphite by at least a factor of 15. Our calculations further indicate that these porous carbon networks possess high storage capacity for gaseous atoms and molecules in agreement with the experiments.A new kind of three-dimensional carbon allotrope, termed carbon honeycomb (CHC), has recently been synthesized [PRL 116, 055501 (2016)]. Based on the experimental results, a family of graphene networks has been constructed, and their electronic and phonon properties are studied by various theoretical approaches. All networks are porous metals with two types of electron transport channels along the honeycomb axis and they are isolated from each other: one type of channel originates from the orbital interactions of the carbon zigzag chains and is topologically protected, while the other type of channel is from the straight lines of the carbon atoms that link the zigzag chains and is topologically trivial. The velocity of the electrons can reach ~106 m s-1. Phonon transport in these allotropes is strongly anisotropic, and the thermal conductivities can be very low when compared with graphite by

  17. Ignition Features of Plasma-Beam Discharge in Gas-Discharge Electron Gun Operation

    Directory of Open Access Journals (Sweden)

    Valery A. Tutyk

    2013-01-01

    Full Text Available The current paper presents the results of experimental researches to determine the mode features of plasma-beam discharge (PBD generation by an electron beam injected by a low-vacuum gasdischarge electron gun (LGEG with the cold cathode and hollow anode on the basis of the high-voltage glow discharge and in the range of helium pressure of P ? 10 ÷ 130 Pa. The PBD boundaries and their dependences on parameters of an electron beam are found. The influence of PBD on parameters of low-vacuum gas-discharge electron gun is revealed. It causes an avalanche increase of electron beam current and burning of plasma-beam discharge in the whole space of the vacuum chamber volume and generation of electromagnetic radiation is revealed. Achieved results will be used for implementation of various vacuum technologies in the medium of reaction gas and generated electromagnetic radiation.

  18. Electrons Mediate the Gas-Phase Oxidation of Formic Acid with Ozone.

    Science.gov (United States)

    van der Linde, Christian; Tang, Wai-Kit; Siu, Chi-Kit; Beyer, Martin K

    2016-08-26

    Gas-phase reactions of CO3 (.-) with formic acid are studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Signal loss indicates the release of a free electron, with the formation of neutral reaction products. This is corroborated by adding traces of SF6 to the reaction gas, which scavenges 38 % of the electrons. Quantum chemical calculations of the reaction potential energy surface provide a reaction path for the formation of neutral carbon dioxide and water as the thermochemically favored products. From the literature, it is known that free electrons in the troposphere attach to O2 , which in turn transfer the electron to O3 . O3 (.-) reacts with CO2 to form CO3 (.-) . The reaction reported here formally closes the catalytic cycle for the oxidation of formic acid with ozone, catalyzed by free electrons.

  19. Observation of Spin Coulomb Drag in a Two-Dimensional Electron Gas

    Energy Technology Data Exchange (ETDEWEB)

    Weber, C.P.

    2011-08-19

    An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin, which offer potential advantages in dissipation, size, and speed over charge-based devices. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (-e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves. In contrast, the electron's spin along a given spatial direction can take on two values, {+-} {h_bar}/2 (conventionally {up_arrow}, {down_arrow}), so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron-electron (e-e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e-e collisions.

  20. A scintillating GEM for 2D-dosimetry in radiation therapy

    CERN Document Server

    Timmer, J; Bom, V; Eijk, C W; Haas, J D; Schippers, J M

    2002-01-01

    The first results of a study on the properties of a gaseous scintillation detector based on a Gas Electron Multiplier (GEM) are reported. The detector is designed for use in position-sensitive dosimetry applications in radiation therapy. A double GEM system, operating in a 90-10% Ar-CO sub 2 gas mixture at a gas amplification factor of approx 3000, emits a sufficient amount of detectable light to perform measurements of approx 1 Gy doses in two dimensions. The light yield does not suffer from quenching processes when particles with high stopping power are detected. This operation mode of GEMs offers the dosimetric advantages of a gas-filled detector and the 2D read-out can be performed with a CCD camera. Compared to the existing dosimeters, this system is relatively simple and no complex multi-electrode read-out is necessary.

  1. Thermal electron attachment to chlorinated alkenes in the gas phase

    Science.gov (United States)

    Wnorowski, K.; Wnorowska, J.; Michalczuk, B.; Jówko, A.; Barszczewska, W.

    2017-01-01

    This paper reports the measurements of the rate coefficients and the activation energies of the electron capture processes with various chlorinated alkenes. The electron attachment processes in the mixtures of chlorinated alkenes with carbon dioxide have been investigated using a Pulsed Townsend technique. This study has been performed in the temperature range (298-378) K. The obtained rate coefficients more or less depended on temperature in accordance to Arrhenius equation. The activation energies (Ea's) were determined from the fit to the experimental data points with function ln(k) = ln(A) - Ea/kBT. The rate coefficients at 298 K were equal to 1.0 × 10-10 cm3 s-1, 2.2 × 10-11 cm3 s-1, 1.6 × 10-9 cm3 s-1, 4.4 × 10-8 cm3 s-1, 2.9 × 10-12 cm3 s-1 and 7.3 × 10-12 cm3 s-1 and activation energies were: 0.27 eV, 0.26 eV, 0.25 eV, 0.21 eV, 0.55 eV and 0.42 eV, for trans-1,2-dichloroethylene, cis-1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, 2-chloropropene, 3-chloropropene respectively.

  2. Development of compact gas treatment system using secondary emission electron gun

    CERN Document Server

    Watanabe, M; Okino, A; Ko, K C; Hotta, E; Watanabe, Masato; Wang, Yu; Okino, Akitoshi; Ko, Kwang-Cheol; Hotta, Eiki

    2004-01-01

    It is well known that the non-thermal plasma processes using electrical discharge or electron beam are effective for the environmental pollutant removal. Especially, the electron beam can efficiently remove pollutant, because a lot of radicals which are useful to remove pollutant can be easily produced by high-energy electrons. We have developed a compact 100kV secondary emission electron gun to apply NOX removal. The device offers several inherent advantages such as compact in size, wide and uniform electron beam. Besides, the device offers good capability in high repetition rate pulsed operation with easy control compared with glow discharge or field emission control cathode guns. In present study, the NOX removal characteristics have been studied under the increased gun voltage, varied pulsed electron beam parameters such as current density and pulse width as well as gas flow rate. The experimental results indicate a better NOX removal efficiency comparing to other high-energy electron beam and electrical ...

  3. Materials science: Screen printing of 2D semiconductors

    Science.gov (United States)

    Kim, Young Duck; Hone, James

    2017-04-01

    Atomically thin semiconductors have been made by transferring the oxide 'skin' of a liquid metal to substrates. This opens the way to the low-cost mass production of 2D semiconductors at the sizes needed for electronics applications.

  4. Enhanced electron yield from laser-driven wakefield acceleration in high-Z gas jets.

    Science.gov (United States)

    Mirzaie, Mohammad; Hafz, Nasr A M; Li, Song; Liu, Feng; He, Fei; Cheng, Ya; Zhang, Jie

    2015-10-01

    An investigation of the electron beam yield (charge) form helium, nitrogen, and neon gas jet plasmas in a typical laser-plasma wakefield acceleration experiment is carried out. The charge measurement is made by imaging the electron beam intensity profile on a fluorescent screen into a charge coupled device which was cross-calibrated with an integrated current transformer. The dependence of electron beam charge on the laser and plasma conditions for the aforementioned gases are studied. We found that laser-driven wakefield acceleration in low Z-gas jet targets usually generates high-quality and well-collimated electron beams with modest yields at the level of 10-100 pC. On the other hand, filamentary electron beams which are observed from high-Z gases at higher densities reached much higher yields. Evidences for cluster formation were clearly observed in the nitrogen gas jet target, where we received the highest electron beam charge of ∼1.7 nC. Those intense electron beams will be beneficial for the applications on the generation of bright X-rays, gamma rays radiations, and energetic positrons via the bremsstrahlung or inverse-scattering processes.

  5. The ionization state in a gas with a non-Maxwellian electron distribution

    Science.gov (United States)

    Owocki, S. P.; Scudder, J. D.

    1981-01-01

    The inferred degree of ionization of a gas is often used in astrophysics as a diagnostic of the gas temperature. In the solar transition region and corona, in the outer atmospheres of cool stars, and in some portions of the interstellar medium), photoionization can be neglected, and the ionization state is fixed by the balance between ion-electron collisional ionization and dielectronic and/or radiative recombination. Under these conditions, higher degrees of ionization result from higher energy ion-electron collisions which are common in a high temperature gas. Actually, ionization occurs through collisions with electrons that have kinetic energies greater than the ionization potential of the given ion, and so the ionization rate depends on to the number of such high-energy electrons in the tail of the electron velocity distribution. High-velocity electrons move across large distances between effective coulomb collisions, and, in a strong temperature or density gradient, the tail can be overpopulated relative to Maxwell-Boltzmann distribution of equivalent energy density. Thus, the ionization rate can also be greatly increased. These effects for a parameterized form of the electron distribution function with an enhanced high-velocity tail, namely the kappa distribution are illustrated.

  6. Enhanced electron yield from laser-driven wakefield acceleration in high-Z gas jets

    Energy Technology Data Exchange (ETDEWEB)

    Mirzaie, Mohammad; Hafz, Nasr A. M., E-mail: nasr@sjtu.edu.cn; Li, Song; Liu, Feng; Zhang, Jie [Key Laboratory for Laser Plasmas (MOE) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China); He, Fei; Cheng, Ya [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)

    2015-10-15

    An investigation of the electron beam yield (charge) form helium, nitrogen, and neon gas jet plasmas in a typical laser-plasma wakefield acceleration experiment is carried out. The charge measurement is made by imaging the electron beam intensity profile on a fluorescent screen into a charge coupled device which was cross-calibrated with an integrated current transformer. The dependence of electron beam charge on the laser and plasma conditions for the aforementioned gases are studied. We found that laser-driven wakefield acceleration in low Z-gas jet targets usually generates high-quality and well-collimated electron beams with modest yields at the level of 10-100 pC. On the other hand, filamentary electron beams which are observed from high-Z gases at higher densities reached much higher yields. Evidences for cluster formation were clearly observed in the nitrogen gas jet target, where we received the highest electron beam charge of ∼1.7 nC. Those intense electron beams will be beneficial for the applications on the generation of bright X-rays, gamma rays radiations, and energetic positrons via the bremsstrahlung or inverse-scattering processes.

  7. Heterodyne Hall effect in a two-dimensional electron gas

    Science.gov (United States)

    Oka, Takashi; Bucciantini, Leda

    2016-10-01

    We study the hitherto unaddressed phenomenon of the quantum Hall effect with a magnetic and electric field oscillating in time with resonant frequencies. This phenomenon highlights an example of a heterodyne device with the magnetic field acting as a driving force, and it is analyzed in detail in its classical and quantum versions using Floquet theory. A bulk current flowing perpendicularly to the applied electric field is found, with a frequency shifted by integer multiples of the driving frequency. When the ratio of the cyclotron and driving frequency takes special values, the electron's classical trajectory forms a loop and the effective mass diverges, while in the quantum case we find an analog of the Landau quantization. A possible realization using metamaterial plasmonics is discussed.

  8. Determination of gas temperature in the plasmatron channel according to the known distribution of electronic temperature

    Directory of Open Access Journals (Sweden)

    Gerasimov Alexander V.

    2013-01-01

    Full Text Available An analytical method to calculate the temperature distribution of heavy particles in the channel of the plasma torch on the known distribution of the electronic temperature has been proposed. The results can be useful for a number of model calculations in determining the most effective conditions of gas blowing through the plasma torch with the purpose of heating the heavy component. This approach allows us to understand full details about the heating of cold gas, inpouring the plasma, and to estimate correctly the distribution of the gas temperature inside the channel.

  9. Electronic properties of NH4-adsorbed graphene nanoribbon as a promising candidate for a gas sensor

    Science.gov (United States)

    Harada, Naoki; Sato, Shintaro

    2016-05-01

    The electronic properties of NH4-adsorbed N = 7 armchair graphene nanoribbons (AGNRs) were theoretically investigated using self-consistent atomistic simulations to explore the feasibility of AGNRs as a gas sensing material. Whereas a pristine AGNR has a finite band gap and is an intrinsic semiconductor, an NH4-adsorbed AGNR exhibits heavily doped n-type properties similar to a graphene sheet with the molecules adsorbed. The electric characteristics of a back-gated AGNR gas sensor were also simulated and the drain current changed exponentially with increasing number of adsorbed molecules. We may conclude that an AGNR is promising as a highly sensitive gas-sensing material with large outputs.

  10. Analysis of the Molecules Structure and Vertical Electron Affinity of Organic Gas Impact on Electric Strength

    Science.gov (United States)

    Jiao, Juntao; Xiao, Dengming; Zhao, Xiaoling; Deng, Yunkun

    2016-05-01

    It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride (SF6). As the properties of gas are determined by the gas molecule structure, the research on the relationship between the gas molecule structure and the electric strength can contribute to the gas pre-screening and new gas development. In this paper, we calculated the vertical electron affinity, molecule orbits distribution and orbits energy of gas molecules by the means of density functional theory (DFT) for the typical structures of organic gases and compared their electric strengths. By this method, we find part of the key properties of the molecule which are related to the electric strength, including the vertical electron affinity, the lowest unoccupied molecule orbit (LUMO) energy, molecule orbits distribution and negative-ion system energy. We also listed some molecule groups such as unsaturated carbons double bonds (C=C) and carbonitrile bonds (C≡N) which have high electric strength theoretically by this method. supported by National Natural Science Foundation of China (Nos. 51177101 and 51337006)

  11. Analysis of the Molecules Structure and Vertical Electron Affinity of Organic Gas Impact on Electric Strength

    Institute of Scientific and Technical Information of China (English)

    JIAO Juntao; XIAO Dengming; ZHAO Xiaoling; DENG Yunkun

    2016-01-01

    It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride (SF6).As the properties of gas are determined by the gas molecule structure,the research on the relationship between the gas molecule structure and the electric strength can contribute to the gas pre-screening and new gas development.In this paper,we calculated the vertical electron affinity,molecule orbits distribution and orbits energy of gas molecules by the means of density functional theory (DFT) for the typical structures of organic gases and compared their electric strengths.By this method,we find part of the key properties of the molecule which are related to the electric strength,including the vertical electron affinity,the lowest unoccupied molecule orbit (LUMO) energy,molecule orbits distribution and negativeion system energy.We also listed some molecule groups such as unsaturated carbons double bonds (C=C) and carbonitrile bonds (C≡N) which have high electric strength theoretically by this method.

  12. Controlled synthesis of 2D transition metal dichalcogenides: from vertical to planar MoS2

    Science.gov (United States)

    Zhang, Fu; Momeni, Kasra; Abu AlSaud, Mohammed; Azizi, Amin; Hainey, Mel F., Jr.; Redwing, Joan M.; Chen, Long-Qing; Alem, Nasim

    2017-06-01

    Among post-graphene two dimensional (2D) materials, transition metal dichalcogenides (TMDs, such as MoS2) have attracted significant attention due to their superior properties for potential electronic, optoelectronic and energy applications. Scalable and controllable powder vapor transport (PVT) methods have been developed to synthesize 2D MoS2 with controllable morphologies (i.e. horizontal and vertical), yet the growth mechanism for the transition from horizontal to vertical orientation is not clearly understood. Here, we combined experimental and numerical modeling studies to investigate the key growth parameters that govern the morphology of 2D materials. The transition from vertical to horizontal growth is achieved by controlling the magnitude and distribution of the precursor concentration by placing the substrate at different orientations and locations relative to the source. We have also shown that the density of as-grown nanostructures can be controlled by the local precursor-containing gas flow rate. This study demonstrates the possibility for engineering the morphology of 2D materials by controlling the concentration of precursors and flow profiles, and provides a new path for controllable growth of 2D TMDs for various applications.

  13. Cosmic Ray Test of Mini-drift Thick Gas Electron Multiplier Chamber for Transition Radiation Detector

    CERN Document Server

    Yang, S; Buck, B; Li, C; Ljubicic, T; Majka, R; Shao, M; Smirnov, N; Visser, G; Xu, Z; Zhou, Y

    2014-01-01

    A thick gas electron multiplier (THGEM) chamber with an effective readout area of 10$\\times$10 cm$^{2}$ and a 11.3 mm ionization gap has been tested along with two regular gas electron multiplier (GEM) chambers in a cosmic ray test system. The thick ionization gap makes the THGEM chamber a mini-drift chamber. This kind mini-drift THGEM chamber is proposed as part of a transition radiation detector (TRD) for identifying electrons at an Electron Ion Collider (EIC) experiment. Through this cosmic ray test, an efficiency larger than 94$\\%$ and a spatial resolution $\\sim$220 $\\mu$m are achieved for the THGEM chamber at -3.65 kV. Thanks to its outstanding spatial resolution and thick ionization gap, the THGEM chamber shows excellent track reconstruction capability. The gain uniformity and stability of the THGEM chamber are also presented.

  14. Transport at low electron density in the two-dimensional electron gas of silicon MOSFETs

    NARCIS (Netherlands)

    Heemskerk, Richard

    1998-01-01

    his thesis contains the result of an experimental study on the transport properties of high quality Si MOSFETs at low temperatures. A metalinsulator transition is found at a critical electron density. The electrons in the inversion layer of a silicon MOSFET are trapped in a potential well at the Si-

  15. Possible evidence for partial demagnetization of electrons in the auroral E-region plasma during electron gas heating

    Directory of Open Access Journals (Sweden)

    C. Haldoupis

    Full Text Available A previous study, based on incoherent and coherent radar measurements, suggested that during auroral E-region electron heating conditions, the electron flow in the auroral electrojet undergoes a systematic counterclockwise rotation of several degrees relative to the E×B direction. The observational evidence is re-examined here in the light of theoretical predictions concerning E-region electron demagnetization caused by enhanced anomalous cross-field diffusion during strongly-driven Farley-Buneman instability. It is shown that the observations are in good agreement with this theory. This apparently endorses the concept of wave-induced diffusion and anomalous electron collision frequency, and consequently electron demagnetization, under circumstances of strong heating of the electron gas in the auroral electrojet plasma. We recognize, however, that the evidence for electron demagnetization presented in this report cannot be regarded as definitive because it is based on a limited set of data. More experimental research in this direction is thus needed.

  16. A New Class of Resonances at the Edge of the Two Dimensional Electron Gas

    OpenAIRE

    Zhitenev, N. B.; Brodsky, M; Ashoori, R. C.; Melloch, M. R.

    1996-01-01

    We measure the frequency dependent capacitance of a gate covering the edge and part of a two-dimensional electron gas in the quantum Hall regime. In applying a positive gate bias, we create a metallic puddle under the gate surrounded by an insulating region. Charging of the puddle occurs via electron tunneling from a metallic edge channel. Analysis of the data allows direct extraction of this tunneling conductance. Novel conductance resonances appear as a function of gate bias. Samples with g...

  17. Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

    Institute of Scientific and Technical Information of China (English)

    YANG Shi-Jie; ZHAO Hu; YU Yue

    2005-01-01

    When a surface acoustic wave (SAW) propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.

  18. Ionization cross sections for electron scattering from metastable rare-gas atoms (Ne* and Ar*)

    Institute of Scientific and Technical Information of China (English)

    Zhang Yong-Zhi; Zhou Ya-Jun

    2013-01-01

    The optical-model approach has been used to investigate the electron-impact ionization of metastable rare-gas atoms.A complex equivalent-local polarization potential is obtained to describe the ionization continuum channels.We have calculated the cross sections for collisional ionization of the metastable atoms Ne* and Ar* by electrons in the energy range from threshold to 200 eV.The present results are in agreement with the available experimental measurements and other theoretical calculations.

  19. An automated pipeline to screen membrane protein 2D crystallization.

    Science.gov (United States)

    Kim, Changki; Vink, Martin; Hu, Minghui; Love, James; Stokes, David L; Ubarretxena-Belandia, Iban

    2010-06-01

    Electron crystallography relies on electron cryomicroscopy of two-dimensional (2D) crystals and is particularly well suited for studying the structure of membrane proteins in their native lipid bilayer environment. To obtain 2D crystals from purified membrane proteins, the detergent in a protein-lipid-detergent ternary mixture must be removed, generally by dialysis, under conditions favoring reconstitution into proteoliposomes and formation of well-ordered lattices. To identify these conditions a wide range of parameters such as pH, lipid composition, lipid-to-protein ratio, ionic strength and ligands must be screened in a procedure involving four steps: crystallization, specimen preparation for electron microscopy, image acquisition, and evaluation. Traditionally, these steps have been carried out manually and, as a result, the scope of 2D crystallization trials has been limited. We have therefore developed an automated pipeline to screen the formation of 2D crystals. We employed a 96-well dialysis block for reconstitution of the target protein over a wide range of conditions designed to promote crystallization. A 96-position magnetic platform and a liquid handling robot were used to prepare negatively stained specimens in parallel. Robotic grid insertion into the electron microscope and computerized image acquisition ensures rapid evaluation of the crystallization screen. To date, 38 2D crystallization screens have been conducted for 15 different membrane proteins, totaling over 3000 individual crystallization experiments. Three of these proteins have yielded diffracting 2D crystals. Our automated pipeline outperforms traditional 2D crystallization methods in terms of throughput and reproducibility.

  20. High current table-top setup for femtosecond gas electron diffraction

    Directory of Open Access Journals (Sweden)

    Omid Zandi

    2017-07-01

    Full Text Available We have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample. We present here a device that uses pulse compression to overcome the Coulomb broadening and deliver femtosecond electron pulses on a gas target. The velocity mismatch can be compensated using laser pulses with a tilted intensity front to excite the sample. The temporal resolution of the setup was determined with a streak camera to be better than 400 fs for pulses with up to half a million electrons and a kinetic energy of 90 keV. The high charge per pulse, combined with a repetition rate of 5 kHz, results in an average beam current that is between one and two orders of magnitude higher than previously demonstrated.

  1. First-principles investigations of metal (V, Nb, Ta)-doped monolayer MoS2: Structural stability, electronic properties and adsorption of gas molecules

    Science.gov (United States)

    Zhu, Jia; Zhang, Hui; Tong, Yawen; Zhao, Ling; Zhang, Yongfan; Qiu, Yuzhi; Lin, Xianning

    2017-10-01

    Two-dimensional (2D) layered materials are at the forefront of research because of their unique structures and promising catalytic abilities. Here, the structural stability, electronic properties and gas adsorption of metal (V, Nb, Ta)-doped monolayer MoS2 have been investigated by density functional theory calculations. Our results show that the metal (V, Nb, Ta)-doped monolayer MoS2 is a stable catalyst under room temperature, due to the strong interaction between the doped metals (V, Nb, Ta) and S vacancy of monolayer MoS2. Compared with the gas adsorption (CO, NO2, H2O, NH3) on pristine monolayer MoS2, doped metal (V, Nb, Ta) can significantly improve the adsorption properties, chemical activity and the sensitivity of that of adsorbed gas molecules. This effect occurs due to the strong overlap between the metal nd orbitals and gas molecule orbitals, result in activation of the adsorbed gas molecules. Analysis of Bader charge shows that, more charge transfer (-0.66 e to -0.72 e) occur from metal (V, Nb, Ta)-doped monolayer MoS2 to the oxidizing gas molecules (NO2) acting as acceptors. While for the adsorption of CO molecules, the relative less electrons (about -0.24 e - -0.35 e) transfer occuring from substrate to the adsorbed gases. Whereas the direction of charge transfers is reversed for the adsorption of the reducing gas (H2O and NH3) behaving as donors, in which small electrons (0.04 e -0.09 e) transfer from adsorbed gas to metal (V, Nb, Ta)-doped monolayer MoS2. Our results suggested that metal (V, Nb, Ta)-doped monolayer MoS2 might be a good candidate for low-cost, highly active, and stable catalysts and gas sensors, providing an avenue to facilitate the design of high active MoS2-based two dimensional catalysts and gas sensors.

  2. Electron density and gas density measurements in a millimeter-wave discharge

    Energy Technology Data Exchange (ETDEWEB)

    Schaub, S. C., E-mail: sschaub@mit.edu; Hummelt, J. S.; Guss, W. C.; Shapiro, M. A.; Temkin, R. J. [Plasma Science and Fusion Center, Massachusetts Institute of Technology 167 Albany St., Bldg. NW16, Cambridge, Massachusetts 02139 (United States)

    2016-08-15

    Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.

  3. Aero Fighter - 2D Gaming

    CERN Document Server

    Ahmed, Zeeshan

    2010-01-01

    Designing and developing quality based computer game is always a challenging task for developers. In this paper I briefly discuss aero fighting war game based on simple 2D gaming concepts and developed in C & C++ programming languages, using old bitmapping concepts. Going into the details of the game development, I discuss the designed strategies, flow of game and implemented prototype version of game, especially for beginners of game programming.

  4. Electron kinetics dependence on gas pressure in laser-induced oxygen plasma experiment: Theoretical analysis

    Science.gov (United States)

    Gamal, Yosr E. E.-D.; Abdellatif, Galila

    2017-08-01

    A study is performed to investigate the dependency of threshold intensity on gas pressure observed in the measurements of the breakdown of molecular oxygen that carried out by Phuoc (2000) [1]. In this experiment, the breakdown was induced by 532 nm laser radiation of pulse width 5.5 ns and spot size of 8.5 μm, in oxygen over a wide pressure range (190-3000 Torr). The analysis aimed to explore the electron kinetic reliance on gas pressure for the separate contribution of each of the gain and loss processes encountered in this study. The investigation is based on an electron cascade model applied previously in Gamal and Omar (2001) [2] and Gaabour et al. (2013) [3]. This model solves numerically a differential equation designates the time evolution of the electron energy distribution, and a set of rate equations that describe the change of excited states population. The numerical examination of the electron energy distribution function and its parameters revealed that photo-ionization of the excited molecules plays a significant role in enhancing the electron density growth rate over the whole tested gas pressure range. This process is off set by diffusion of electrons out of the focal volume in the low-pressure regime. At atmospheric pressure electron, collisional processes dominate and act mainly to populate the excited states. Hence photo-ionization becomes efficient and compete with the encountered loss processes (electron diffusion, vibrational excitation of the ground state molecules as well as two body attachments). At high pressures ( 3000 Torr) three body attachments are found to be the primary cause of losses which deplete the electron density and hence results in the slow decrease of the threshold intensity.

  5. Analysis and design of digital output interface devices for gas turbine electronic controls

    Science.gov (United States)

    Newirth, D. M.; Koenig, E. W.

    1976-01-01

    A trade study was performed on twenty-one digital output interface schemes for gas turbine electronic controls to select the most promising scheme based on criteria of reliability, performance, cost, and sampling requirements. The most promising scheme, a digital effector with optical feedback of the fuel metering valve position, was designed.

  6. Direct Measurement of the Band Structure of a Buried Two-Dimensional Electron Gas

    DEFF Research Database (Denmark)

    Miwa, Jill; Hofmann, Philip; Simmons, Michelle Y.;

    2013-01-01

    We directly measure the band structure of a buried two dimensional electron gas (2DEG) using angle resolved photoemission spectroscopy. The buried 2DEG forms 2 nm beneath the surface of p-type silicon, because of a dense delta-type layer of phosphorus n-type dopants which have been placed there. ...

  7. Fireworks in noble gas clusters a first experiment with the new "free-electron laser"

    CERN Multimedia

    2002-01-01

    An international group of scientists has published first experiments carried out using the new soft X-ray free-electron laser (FEL) at the research center DESY in Hamburg, Germany. Using small clusters of noble gas atoms, for the first time, researchers studied the interaction of matter with intense X-ray radiation from an FEL on extremely short time scales (1 page).

  8. Model for ballistic spin-transport in ferromagnet/two-dimensional electron gas/ferromagnet structures

    NARCIS (Netherlands)

    Schapers, T; Nitta, J; Heersche, HB; Takayanagi, H

    2002-01-01

    The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two

  9. High-energy electron acceleration in the gas-puff Z-pinch plasma

    Science.gov (United States)

    Takasugi, Keiichi; Miyazaki, Takanori; Nishio, Mineyuki

    2014-12-01

    The characteristics of hard x-ray generation were examined in the gas-puff z-pinch experiment. The experiment on reversing the voltage was conducted. In both of the positive and negative discharges, the x-ray was generated only from the anode surface, so it was considered that the electrons were accelerated by the induced electromagnetic force at the pinch time.

  10. Structure analysis of large argon clusters from gas-phase electron diffraction data: some recent results

    NARCIS (Netherlands)

    Waal, van de B.W.

    1999-01-01

    An up-to-date overview of recent developments in the structure elucidation of large ArN-clusters (103gas-phase electron diffraction data, is given. Although a satisfactory model for N3000 had been found in 1996, the size range beyond N10,000 presents new and unexpected problems. T

  11. High-energy electron acceleration in the gas-puff Z-pinch plasma

    Energy Technology Data Exchange (ETDEWEB)

    Takasugi, Keiichi, E-mail: takasugi@phys.cst.nihon-u.ac.jp [Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda, Tokyo 101-8308 (Japan); Miyazaki, Takanori [Institute of Quantum Science, Nihon University, 1-8 Kanda-Surugadai, Chiyoda, Tokyo 101-8308, Japan and Dept. Innovation Systems Eng., Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585 (Japan); Nishio, Mineyuki [Anan National College of Technology, 265 Aoki, Minobayashi, Anan, Tokushima 774-0017 (Japan)

    2014-12-15

    The characteristics of hard x-ray generation were examined in the gas-puff z-pinch experiment. The experiment on reversing the voltage was conducted. In both of the positive and negative discharges, the x-ray was generated only from the anode surface, so it was considered that the electrons were accelerated by the induced electromagnetic force at the pinch time.

  12. Model of two-dimensional electron gas formation at ferroelectric interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Aguado-Puente, P.; Bristowe, N. C.; Yin, B.; Shirasawa, R.; Ghosez, Philippe; Littlewood, P. B.; Artacho, Emilio

    2015-07-01

    The formation of a two-dimensional electron gas at oxide interfaces as a consequence of polar discontinuities has generated an enormous amount of activity due to the variety of interesting effects it gives rise to. Here, we study under what circumstances similar processes can also take place underneath ferroelectric thin films. We use a simple Landau model to demonstrate that in the absence of extrinsic screening mechanisms, a monodomain phase can be stabilized in ferroelectric films by means of an electronic reconstruction. Unlike in the LaAlO3/SrTiO3 heterostructure, the emergence with thickness of the free charge at the interface is discontinuous. This prediction is confirmed by performing first-principles simulations of free-standing slabs of PbTiO3. The model is also used to predict the response of the system to an applied electric field, demonstrating that the two-dimensional electron gas can be switched on and off discontinuously and in a nonvolatile fashion. Furthermore, the reversal of the polarization can be used to switch between a two-dimensional electron gas and a two-dimensional hole gas, which should, in principle, have very different transport properties. We discuss the possible formation of polarization domains and how such configuration competes with the spontaneous accumulation of free charge at the interfaces.

  13. Identification and measurement of chlorinated organic pesticides in water by electron-capture gas chromatography

    Science.gov (United States)

    Lamar, William L.; Goerlitz, Donald F.; Law, LeRoy M.

    1965-01-01

    Pesticides, in minute quantities, may affect the regimen of streams, and because they may concentrate in sediments, aquatic organisms, and edible aquatic foods, their detection and their measurement in the parts-per-trillion range are considered essential. In 1964 the U.S. Geological Survey at Menlo Park, Calif., began research on methods for monitoring pesticides in water. Two systems were selected--electron-capture gas chromatography and microcoulometric-titration gas chromatography. Studies on these systems are now in progress. This report provides current information on the development and application of an electron-capture gas chromatographic procedure. This method is a convenient and extremely sensitive procedure for the detection and measurement of organic pesticides having high electron affinities, notably the chlorinated organic pesticides. The electron-affinity detector is extremely sensitive to these substances but it is not as sensitive to many other compounds. By this method, the chlorinated organic pesticide may be determined on a sample of convenient size in concentrations as low as the parts-per-trillion range. To insure greater accuracy in the identifications, the pesticides reported were separated and identified by their retention times on two different types of gas chromatographic columns.

  14. Gas electron multiplier based on laser-perforated CVD diamond film: First tests

    CERN Document Server

    Franchino, S; Bolshakov, A; Ashkinazi, E; Kalkan, Y; Popovich, A; Komlenok, M; Sosnovtsev, V; Ralchenko, V

    2016-01-01

    Gas electron multiplier (GEM) is widely used in modern gas detectors of ionizing radiation in experiments on high-energy physics at accelerators and in other fields of science. Typically the GEM devices are based on a dielectric foil with holes and electrodes on both sides. GEMs made by radiation-hard dielectrics or wide band-gap semiconductors are desirable for some applications. The results of the first tests of the gas electron multiplier made of radiation-hard materials, such as polycrystalline CVD diamond with a thickness of 100 microns is described. Here we report on fabrication of GEM based on free-standing polycrystalline CVD diamond film and its first test.

  15. The study of electronic structure and properties of silicene for gas sensor application

    Science.gov (United States)

    Wella, Sasfan A.; Syaputra, Marhamni; Wungu, Triati D. K.; Suprijadi

    2016-03-01

    In this study, we investigated the adsorption of gas molecules (H2S, CO) on pristine silicene using first principles calculation. The structure, electronic properties, and adsorption energy of H2S,CO/silicene are discussed thoroughly. We found that the pristine silicenewith low buckling structure is the most stable as compared with planar and high buckling structures. Silicene was able to detect a gas molecule which can be observed according tothe density of states analysis. Though a gas molecule adsorbed weakly, the electronic properties of the low buckling pristine silicene changed from semi-metal (zero band gap) to semiconductor. The adsorption energy of H2S and CO on silicene is 0.075 eV and 0.06 eV, respectively.

  16. Polyoxometalate-mediated electron transfer-oxygen transfer oxidation of cellulose and hemicellulose to synthesis gas.

    Science.gov (United States)

    Sarma, Bidyut Bikash; Neumann, Ronny

    2014-08-01

    Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen.

  17. Photon-assisted spin transport in a two-dimensional electron gas

    OpenAIRE

    Fistul, M. V.; Efetov, K. B.

    2007-01-01

    We study spin-dependent transport in a two-dimensional electron gas subject to an external step-like potential $V(x)$ and irradiated by an electromagnetic field (EF). In the absence of EF the electronic spectrum splits into spin sub-bands originating from the "Rashba" spin-orbit coupling. We show that the resonant interaction of propagating electrons with the component EF parallel to the barrier induces a \\textit{% non-equilibrium dynamic gap} $(2\\Delta_{R})$ between the spin sub-bands. Exist...

  18. High efficiency noble gas electron impact ion source for isotope separation

    Energy Technology Data Exchange (ETDEWEB)

    Appelhans, A. D. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Olson, J. E. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Dahl, D. A. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Ward, M. B. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-07-01

    An electron impact ion source has been designed for generation of noble gas ions in a compact isotope separator. The source utilizes a circular filament that surrounds an ionization chamber, enabling multiple passes of electrons through the ionization chamber. This report presents ion optical design and the results of efficiency and sensitivity measurements performed in an ion source test chamber and in the compact isotope separator. The cylindrical design produced xenon ions at an efficiency of 0.37% with a sensitivity of ~24 µA /Pa at 300 µA of electron current.

  19. Extraordinary waves in two dimensional electron gas with separate spin evolution and Coulomb exchange interaction

    CERN Document Server

    Andreev, Pavel A

    2016-01-01

    Hydrodynamics analysis of waves in two-dimensional degenerate electron gas with the account of separate spin evolution is presented. The transverse electric field is included along with the longitudinal electric field. The Coulomb exchange interaction is included in the analysis. In contrast with the three-dimensional plasma-like mediums the contribution of the transverse electric field is small. We show the decrease of frequency of both the extraordinary (Langmuir) wave and the spin-electron acoustic wave due to the exchange interaction. Moreover, spin-electron acoustic wave has negative dispersion at the relatively large spin-polarization. Corresponding dispersion dependencies are presented and analyzed.

  20. Hose Instability and Wake Generation By An Intense Electron Beam in a Self-Ionized Gas

    Energy Technology Data Exchange (ETDEWEB)

    Deng, S.; Barnes, C.D.; Clayton, C.E.; O' Connell, C.; Decker, F.J.; Fonseca, R.A.; Huang, C.; Hogan, M.J.; Iverson, R.; Johnson, D.K.; Joshi, C.; Katsouleas, T.; Krejcik,; Lu, W.; Mori, W.B.; Muggli, P.; Oz, E.; Tsung, F.; Walz, D.; Zhou, M.; /Southern California U. /UCLA /SLAC

    2006-04-12

    The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested.

  1. 2dF mechanical engineering

    Science.gov (United States)

    Smith, Greg; Lankshear, Allan

    1998-07-01

    2dF is a multi-object instrument mounted at prime focus at the AAT capable of spectroscopic analysis of 400 objects in a single 2 degree field. It also prepares a second 2 degree 400 object field while the first field is being observed. At its heart is a high precision robotic positioner that places individual fiber end magnetic buttons on one of two field plates. The button gripper is carried on orthogonal gantries powered by linear synchronous motors and contains a TV camera which precisely locates backlit buttons to allow placement in user defined locations to 10 (mu) accuracy. Fiducial points on both plates can also be observed by the camera to allow repeated checks on positioning accuracy. Field plates rotate to follow apparent sky rotation. The spectrographs both analyze light from the 200 observing fibers each and back- illuminate the 400 fibers being re-positioned during the observing run. The 2dF fiber position and spectrograph system is a large and complex instrument located at the prime focus of the Anglo Australian Telescope. The mechanical design has departed somewhat from the earlier concepts of Gray et al, but still reflects the audacity of those first ideas. The positioner is capable of positioning 400 fibers on a field plate while another 400 fibers on another plate are observing at the focus of the telescope and feeding the twin spectrographs. When first proposed it must have seemed like ingenuity unfettered by caution. Yet now it works, and works wonderfully well. 2dF is a system which functions as the result of the combined and coordinated efforts of the astronomers, the mechanical designers and tradespeople, the electronic designers, the programmers, the support staff at the telescope, and the manufacturing subcontractors. The mechanical design of the 2dF positioner and spectrographs was carried out by the mechanical engineering staff of the AAO and the majority of the manufacture was carried out in the AAO workshops.

  2. Preliminary results of the Gas Electron Multiplier (GEM) as real-time beam monitor in hadron therapy

    Science.gov (United States)

    Aza, E.; Ciocca, M.; Murtas, F.; Puddu, S.; Pullia, M.; Silari, M.

    2017-01-01

    The use of proton and carbon ion beams in cancer therapy (also known as hadron therapy) is progressively growing worldwide due to their improved dose distributions, sparing of healthy tissues and (for carbon ions) increased radiobiological effectiveness especially for radio-resistant tumours. Strict Quality Assurance (QA) protocols need to be followed for guaranteeing the clinical beam specifications. The aim of this study was to assess the performance of a gaseous detector based on the Gas Electron Multiplier (GEM) technology for measuring the beam spot dimensions and the homogeneity of the scanned irradiation field, which are daily QA tasks commonly performed using radiochromic films. Measurements performed at the National Centre for Oncological Hadron Therapy (CNAO) in Pavia (Italy) showed that the detector is able to monitor the 2D beam image on-line with a pad granularity of 2 mm and a response proportional to the number of delivered particles. The dose homogeneity was measured with low deviation from the results obtained with radiochromic films.

  3. Applications of Doppler Tomography in 2D and 3D

    Science.gov (United States)

    Richards, M.; Budaj, J.; Agafonov, M.; Sharova, O.

    2010-12-01

    Over the past few years, the applications of Doppler tomography have been extended beyond the usual calculation of 2D velocity images of circumstellar gas flows. This technique has now been used with the new Shellspec spectrum synthesis code to demonstrate the effective modeling of the accretion disk and gas stream in the TT Hya Algol binary. The 2D tomography procedure projects all sources of emission onto a single central (Vx, Vy) velocity plane even though the gas is expected to flow beyond that plane. So, new 3D velocity images were derived with the Radioastronomical Approach method by assuming a grid of Vz values transverse to the central 2D plane. The 3D approach has been applied to the U CrB and RS Vul Algol-type binaries to reveal substantial flow structures beyond the central velocity plane.

  4. Spectrum of fast electrons in a dense gas in the presence of a nonuniform pulsed field

    Science.gov (United States)

    Tkachev, A. N.; Yakovlenko, S. I.

    2007-01-01

    The problems of gas preionization in discharges related to laser physics are considered. The propagation of fast electrons injected from the cathode in the presence of a nonuniform nonstationary field and the motion of multiplying electrons at the edge of the avalanche in the presence of a nonuniform nonstationary field are simulated. The effect of the voltage pulse steepness and the field nonuniformity on the mean propagation velocity of fast electrons and their energy distribution is demonstrated. At certain combinations of the voltage pulse rise time and amplitude and at a certain time interval, the center of gravity of the electron cloud can move in the opposite direction relative to the direction of force acting upon electrons. It is also demonstrated that the number of hard particles (and, hence, the hard component of the x-ray bremsstrahlung) increases with both an increase in the voltage amplitude and a decrease in the pulse rise time. For nonoptimal conditions of the picosecond voltage pulse, an assumption is formulated: an electron beam in gas is formed due to the electrons at the edge of the avalanche rather than the background multiplication wave approaching the anode.

  5. Mechanism to generate a two-dimensional electron gas at the surface of the charge-ordered semiconductor BaBiO3.

    Science.gov (United States)

    Vildosola, Verónica; Güller, Francisco; Llois, Ana María

    2013-05-17

    In this Letter, we find by means of first-principles calculations a new physical mechanism to generate a two-dimensional electron gas, namely, the breaking of charge ordering at the surface of a charge-ordered semiconductor due to the incomplete oxygen environment of the surface ions. The emergence of the 2D gas is independent of the presence of oxygen vacancies or polar discontinuities; this is a self-doping effect. This mechanism might apply to many charge-ordered systems, in particular, we study the case of BaBiO(3)(001). Our calculations show that the outer layer of the Bi-terminated simulated surface turns more cubiclike and metallic while the inner layers remain in the insulating monoclinic state that the system present in the bulk form. On the other hand, the metallization does not occur for the Ba termination, a fact that makes this system appealing for nanostructuring. Finally, in view of the bulk properties of this material under doping, this particular finding sets another possible route for future exploration: the potential scenario of 2D superconductivity at the BaBiO(3) surface.

  6. Implementation of variable time step stochastic dynamics for electronically inelastic gas-surface collisions

    Science.gov (United States)

    Garrett, Bruce C.; Swaminathan, P. K.; Murthy, C. S.; Redmon, Michael J.

    1987-01-01

    A variable time step algorithm has been implemented for solving the stochastic equations of motion for gas-surface collisions. It has been tested for a simple model of electronically inelastic collisions with an insulator surface in which the phonon manifold acts as a heat bath and electronic states are localized. In addition to reproducing the accurate nuclear dynamics of the surface atoms, numerical calculations have shown the algorithm to yield accurate ensemble averages of physical observables such as electronic transition probabilities and total energy loss of the gas atom to the surface. This new algorithm offers a gain in efficieny of up to an order of magnitude compared to fixed time step integration.

  7. Ab Initio Quantum Monte Carlo Simulation of the Warm Dense Electron Gas in the Thermodynamic Limit

    Science.gov (United States)

    Dornheim, Tobias; Groth, Simon; Sjostrom, Travis; Malone, Fionn D.; Foulkes, W. M. C.; Bonitz, Michael

    2016-10-01

    We perform ab initio quantum Monte Carlo (QMC) simulations of the warm dense uniform electron gas in the thermodynamic limit. By combining QMC data with the linear response theory, we are able to remove finite-size errors from the potential energy over the substantial parts of the warm dense regime, overcoming the deficiencies of the existing finite-size corrections by Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)]. Extensive new QMC results for up to N =1000 electrons enable us to compute the potential energy V and the exchange-correlation free energy Fxc of the macroscopic electron gas with an unprecedented accuracy of |Δ V |/|V |,|Δ Fxc|/|F |xc˜10-3 . A comparison of our new data to the recent parametrization of Fxc by Karasiev et al. [Phys. Rev. Lett. 112, 076403 (2014)] reveals significant deviations to the latter.

  8. Many-body quantum chemistry for the electron gas: convergent perturbative theories

    CERN Document Server

    Shepherd, James J

    2013-01-01

    We investigate the accuracy of a number of wavefunction based methods at the heart of quantum chemistry for metallic systems. Using Hartree-Fock as a reference, perturbative (M{\\o}ller-Plesset, MP) and coupled cluster (CC) theories are used to study the uniform electron gas model. Our findings suggest that non-perturbative coupled cluster theories are acceptable for modelling electronic interactions in metals whilst perturbative coupled cluster theories are not. Using screened interactions, we propose a simple modification to the widely-used coupled-cluster singles and doubles plus perturbative triples method (CCSD(T)) that lifts the divergent behaviour and is shown to give very accurate correlation energies for the homogeneous electron gas.

  9. Formation and Dynamics of Vortex Structures in Pure and Gas-Discharge Nonneutral Collisionless Electron Plasmas

    CERN Document Server

    Kervalishvili, N A

    2013-01-01

    The comparative analysis of the results of experimental investigations of the processes of formation, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas taking place for the period of time much less than the electron-neutral collision time has been given. The general processes of formation and behavior of vortex structures in these two plasmas were considered. The phenomena, taking place only in one of these plasmas were also considered. It is shown that the existing difference in behavior of vortex structures is caused by different initial states of nonneutral electron plasmas. The role of vortex structures in the processes taking place in nonneutral electron plasma is discussed.

  10. Head First 2D Geometry

    CERN Document Server

    Fallow), Stray

    2009-01-01

    Having trouble with geometry? Do Pi, The Pythagorean Theorem, and angle calculations just make your head spin? Relax. With Head First 2D Geometry, you'll master everything from triangles, quads and polygons to the time-saving secrets of similar and congruent angles -- and it'll be quick, painless, and fun. Through entertaining stories and practical examples from the world around you, this book takes you beyond boring problems. You'll actually use what you learn to make real-life decisions, like using angles and parallel lines to crack a mysterious CSI case. Put geometry to work for you, and

  11. Relativistic electron gas: A candidate for nature's left-handed materials

    Science.gov (United States)

    de Carvalho, C. A. A.

    2016-05-01

    The electric permittivities and magnetic permeabilities for a relativistic electron gas are calculated from quantum electrodynamics at finite temperature and density as functions of temperature, chemical potential, frequency, and wave vector. The polarization and the magnetization depend linearly on both electric and magnetic fields, and are the sum of a zero-temperature and zero-density vacuum part with a temperature- and chemical-potential-dependent medium part. Analytic calculations lead to generalized expressions that depend on three scalar functions. In the nonrelativistic limit, results reproduce the Lindhard formula. In the relativistic case, and in the long wavelength limit, we obtain the following: (i) for ω =0 , generalized susceptibilities that reduce to known nonrelativistic limits; (ii) for ω ≠0 , Drude-type responses at zero temperature. The latter implies that both the electric permittivity ɛ and the magnetic permeability μ may be simultaneously negative, a behavior characteristic of metamaterials. This unambiguously indicates that the relativistic electron gas is one of nature's candidates for the realization of a negative index of refraction system. Moreover, Maxwell's equations in the medium yield the dispersion relation and the index of refraction of the electron gas. Present results should be relevant for plasma physics, astrophysical observations, synchrotrons, and other environments with fast-moving electrons.

  12. Effect of electron irradiation on gas sensing properties of Al-Zno

    OpenAIRE

    Sunil C. Vattappalam; Deepu Thomas; Simon Augustine; Sunny Mathew

    2015-01-01

    Al–ZnO thin films are prepared by Silar method and are annealed at 450°C for 1 h. A selected number of samples are irradiated by high-energy electron beam and all are characterized by XRD, SEM and energy-dispersive X-ray spectroscopy. Both irradiated and non-irradiated samples are then placed independently inside a gas chamber kept at rotary vacuum. The gas chamber is maintained at a pressure of 0.20 mb and at a temperature of 350°C. Ethanol vapour is admitted in a controlled manner into the ...

  13. Electron attachment to oxygen, water, and methanol, in various drift chamber gas mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Huk, M.; Igo-Kemenes, P.; Wagner, A.

    1988-04-15

    Attachment of electrons to oxygen, water, and methanol molecules has been studied in various gas mixtures based on argon, methane and isobutane, a class of gases often used to operate large drift chambers. The measurements were performed using a drift chamber in which the conditions prevailing in large experiments could be closely reproduced. Attachment coefficients were extracted as a function of the gas composition and pressure, the drift field, and the concentration of the molecules under investigation. The observed effects are compared to other measurements, and are discussed within the frame of physical models. (orig.)

  14. Electron attachment to oxygen, water, and methanol, in various drift chamber gas mixtures

    Science.gov (United States)

    Huk, M.; Igo-Kemenes, P.; Wagner, A.

    1988-04-01

    Attachment of electrons to oxygen, water, and methanol molecules has been studied in various gas mixtures based on argon, methane and isobutane, a class of gases often used to operate large drift chambers. The measurements were performed using a drift chamber in which the conditions prevailing in large experiments could be closely reproduced. Attachment coefficients were extracted as a function of the gas composition and pressure, the drift field, and the concentration of the molecules under investigation. The observed effects are compared to other measurements, and are discussed within the frame of physical models.

  15. A Sealed, UHV Compatible, Soft X-ray Detector Utilizing Gas Electron Multipliers

    Energy Technology Data Exchange (ETDEWEB)

    Schaknowski, N.A.; Smith, G.

    2009-10-25

    An advanced soft X-ray detector has been designed and fabricated for use in synchrotron experiments that utilize X-ray absorption spectroscopy in the study a wide range of materials properties. Fluorescence X-rays, in particular C{sub K} at 277eV, are converted in a low pressure gas medium, and charge multiplication occurs in two gas electron multipliers, fabricated in-house from glass reinforced laminate, to enable single photon counting. The detector satisfies a number of demanding characteristics often required in synchrotron environments, such as UHV compatibility compactness, long-term stability, and energy resolving capability.

  16. Construction of a Gas Electron Multiplier (GEM) Detector for Medical Imaging

    OpenAIRE

    2013-01-01

    A prototype Gas Electron Multiplier (GEM) detector is under construction for medical imaging purposes. A single thick GEM of size 10x10 cm^2 is assembled inside a square shaped air-tight box which is made of Perspex glass. In order to ionize gas inside the drift field two types of voltage supplier circuits were fabricated, and array of 2x4 pads of each size 4x8 mm^2 were utilized for collecting avalanche charges. Preliminary testing results show that the circuit which produces high voltage an...

  17. Fullerene-rare gas mixed plasmas in an electron cyclotron resonance ion source

    CERN Document Server

    Asaji, T; Uchida, T; Minezaki, H; Ishihara, S; Racz, R; Muramatsu, M; Biri, S; Kitagawa, A; Kato, Y; Yoshida, Y

    2015-01-01

    A synthesis technology of endohedral fullerenes such as Fe@C60 has developed with an electron cyclotron resonance (ECR) ion source. The production of N@C60 was reported. However, the yield was quite low, since most fullerene molecules were broken in the ECR plasma. We have adopted gas-mixing techniques in order to cool the plasma and then reduce fullerene dissociation. Mass spectra of ion beams extracted from fullerene-He, Ar or Xe mixed plasmas were observed with a Faraday cup. From the results, the He gas mixing technique is effective against fullerene destruction.

  18. 2D superconductivity by ionic gating

    Science.gov (United States)

    Iwasa, Yoshi

    2D superconductivity is attracting a renewed interest due to the discoveries of new highly crystalline 2D superconductors in the past decade. Superconductivity at the oxide interfaces triggered by LaAlO3/SrTiO3 has become one of the promising routes for creation of new 2D superconductors. Also, the MBE grown metallic monolayers including FeSe are also offering a new platform of 2D superconductors. In the last two years, there appear a variety of monolayer/bilayer superconductors fabricated by CVD or mechanical exfoliation. Among these, electric field induced superconductivity by electric double layer transistor (EDLT) is a unique platform of 2D superconductivity, because of its ability of high density charge accumulation, and also because of the versatility in terms of materials, stemming from oxides to organics and layered chalcogenides. In this presentation, the following issues of electric filed induced superconductivity will be addressed; (1) Tunable carrier density, (2) Weak pinning, (3) Absence of inversion symmetry. (1) Since the sheet carrier density is quasi-continuously tunable from 0 to the order of 1014 cm-2, one is able to establish an electronic phase diagram of superconductivity, which will be compared with that of bulk superconductors. (2) The thickness of superconductivity can be estimated as 2 - 10 nm, dependent on materials, and is much smaller than the in-plane coherence length. Such a thin but low resistance at normal state results in extremely weak pinning beyond the dirty Boson model in the amorphous metallic films. (3) Due to the electric filed, the inversion symmetry is inherently broken in EDLT. This feature appears in the enhancement of Pauli limit of the upper critical field for the in-plane magnetic fields. In transition metal dichalcogenide with a substantial spin-orbit interactions, we were able to confirm the stabilization of Cooper pair due to its spin-valley locking. This work has been supported by Grant-in-Aid for Specially

  19. Investigation of Vortex Structures in Gas-Discharge Nonneutral Electron Plasma: III. Pulse Ejection of Electrons at the Formation and Radial Oscillations of Vortex Structure

    CERN Document Server

    Kervalishvili, N A

    2015-01-01

    The results of experimental investigations of electron ejection from gas-discharge nonneutral electron plasma at the formation and radial oscillations of vortex structure have been presented. The electrons are injected from the vortex structure and the adjacent region of electron sheath in the form of pulses the duration and periodicity of which are determined by the processes of evolution and dynamics of this structure. The possible mechanisms of pulse ejection of electrons are considered. The influence of electron ejection on other processes in discharge electron sheath is analyzed.

  20. Two-dimensional coupled electron-hole layers in high magnetic fields

    NARCIS (Netherlands)

    Parlangeli, Andrea

    2000-01-01

    In solids, it is nowadays possible to create structures in which electrons are confined into a two-dimensional (2D) plane. The physics of a 2D electron gas (2DEG) has proved to be very rich, in particular in the presence of a transverse magnetic field. The Quantum Hall Effect, i.e. the quantization

  1. Molecular structure of cotinine studied by gas electron diffraction combined with theoretical calculations

    Science.gov (United States)

    Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro

    2007-09-01

    The molecular structure of cotinine (( S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone), the major metabolite of nicotine, has been determined at about 182 °C by gas electron diffraction combined with MP2 and DFT calculations. The diffraction data are consistent with the existence of the (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers, where ax and eq indicate the configuration of the pyrrolidinone ring by means of the position (axial and equatorial) of the pyridine ring, and sc, sp and ap distinguish the isomers arising from the internal rotation around the bond connecting the two rings. The (CH 3)NCCC(N) dihedral angles, ϕ, of the (ax, sc) and (eq, sp) conformers were determined independently to be 158(12)° and 129(13)°, respectively, where the numbers in parentheses are three times the standard errors, 3 σ. According to the MP2 calculations, the corresponding dihedral angles for the (ax, ap) and (eq, ap) conformers were assumed to differ by 180° from their syn counterparts. The ratios x(ax, sc)/ x(ax, ap) and x(eq, sp)/ x(eq, ap) were taken from the theoretically estimated free energy differences, Δ G, where x is the abundance of the conformer. The resultant abundances of (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers are 34(6)%, 21% (d.p.), 28% (d.p.), and 17% (d.p.), respectively, where d.p. represents dependent parameters. The determined structural parameters ( rg (Å) and ∠ α (°)) of the most abundant conformer, (ax, sc), are as follows: r(N sbnd C) pyrrol = 1.463(5); r(N sbnd C methyl) = 1.457(←); r(N sbnd C( dbnd O)) = 1.384(12); r(C dbnd O) = 1.219(5); = 1.541(3); r(C pyrrolsbnd C pyrid) = 1.521(←); = 1.396(2); = 1.343(←); ∠(CNC) pyrrol = 113.9(11); ∠CCC pyrrol(-C pyrid) = 103.6(←); ∠NCO = 124.1(13); ∠NC pyrrolC pyrid = 113.1(12); ∠C pyrrolC pyrrolC pyrid = 113.3(←); ∠(CNC) pyrid = 117.1(2); = 124.4(←); ∠C methylNC( dbnd O) = ∠C methylNC(-C pyrid) = 122.8(d.p.); ∠NC( dbnd O)C = 107.1(d.p.); ∠NC pyrrol

  2. Prospects for applications of electron beams in processing of gas and oil hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Ponomarev, A. V., E-mail: ponomarev@ipc.rssi.ru [Russian Academy of Sciences, Frumkin Institute of Physical Chemistry and Electrochemistry (Russian Federation); Pershukov, V. A. [ROSATOM National Nuclear Corporation (Russian Federation); Smirnov, V. P. [CJSC “Nauka i Innovatsii” (Russian Federation)

    2015-12-15

    Waste-free processing of oil and oil gases can be based on electron-beam technologies. Their major advantage is an opportunity of controlled manufacturing of a wide range of products with a higher utility value at moderate temperatures and pressures. The work considers certain key aspects of electron beam technologies applied for the chain cracking of heavy crude oil, for the synthesis of premium gasoline from oil gases, and also for the hydrogenation, alkylation, and isomerization of unsaturated oil products. Electronbeam processing of oil can be embodied via compact mobile modules which are applicable for direct usage at distant oil and gas fields. More cost-effective and reliable electron accelerators should be developed to realize the potential of electron-beam technologies.

  3. Study of the mechanism of increasing production of [KH*2D]exploitation coal bed methane by gas injection%注气开采煤层气增产机制的研究

    Institute of Scientific and Technical Information of China (English)

    吴世跃; 郭勇义

    2001-01-01

    依据扩散渗流和多组分吸附平衡理论,研究了注气开采煤层气的增产机制.研究表明,注气增加储层能量,提高储层压力传导系数并产生竞争吸附置换效应,从而提高煤层气开采时的单产量及回收率.文中还导出了注气时回收率的计算公式.所得结论对注气开采煤层气设计和评价具有指导意义.%According to theory of diffusion and permeation,and theory of adsorpt ion equilibrium of commixture gas,the mechanism of increasing coalbed methane production by gas injection is studied, with which it is illustrated for enhancing energy of storing gas stratum, heightening pressure conduction coefficient of storing gas stratum and binging domino effect of competition adsorption by gas injection, consequently yield and ratio of recovery of coal bed methane are also enhanced. The calculation formulas of ratio of recovery are deduced. These conclusions have guidance significance to exploitation coalbed methane by gas injection.

  4. Personalized 2D color maps

    KAUST Repository

    Waldin, Nicholas

    2016-06-24

    2D color maps are often used to visually encode complex data characteristics such as heat or height. The comprehension of color maps in visualization is affected by the display (e.g., a monitor) and the perceptual abilities of the viewer. In this paper we present a novel method to measure a user\\'s ability to distinguish colors of a two-dimensional color map on a given monitor. We show how to adapt the color map to the user and display to optimally compensate for the measured deficiencies. Furthermore, we improve user acceptance of the calibration procedure by transforming the calibration into a game. The user has to sort colors along a line in a 3D color space in a competitive fashion. The errors the user makes in sorting these lines are used to adapt the color map to his perceptual capabilities.

  5. 2D SIMPLIFIED SERVO VALVE

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A novel pilot stage valve called simplified 2D valve, which utilizes both rotary and linear motions of a single spool, is presented.The rotary motion of the spool incorporating hydraulic resistance bridge, formed by a damper groove and a crescent overlap opening, is utilized as pilot to actuate linear motion of the spool.A criterion for stability is derived from the linear analysis of the valve.Special experiments are designed to acquire the mechanical stiffness, the pilot leakage and the step response.It is shown that the sectional size of the spiral groove affects the dynamic response and the stiffness contradictorily and is also very sensitive to the pilot leakage.Therefore, it is necessary to establish a balance between the static and dynamic characteristics in deciding the structural parameters.Nevertheless, it is possible to sustain the dynamic response at a fairly high level, while keeping the leakage of the pilot stage at an acceptable level.

  6. Developments in Stochastic Coupled Cluster Theory: The initiator approximation and application to the Uniform Electron Gas

    CERN Document Server

    Spencer, James S

    2015-01-01

    We describe further details of the Stochastic Coupled Cluster method and a diagnostic of such calculations, the shoulder height, akin to the plateau found in Full Configuration Interaction Quantum Monte Carlo. We describe an initiator modification to Stochastic Coupled Cluster Theory and show that initiator calculations can be extrapolated to the unbiased limit. We apply this method to the 3D 14-electron uniform electron gas and present complete basis set limit values of the CCSD and previously unattainable CCSDT correlation energies for up to rs = 2, showing a requirement to include triple excitations to accurately calculate energies at high densities.

  7. Towards understanding the influence of electron-gas interactions on imaging in an environmental TEM

    DEFF Research Database (Denmark)

    Wagner, Jakob Birkedal; Boothroyd, Chris; Beleggia, Marco

    2011-01-01

    The latest generation of environmental transmission electron microscopes (ETEMs) incorporates aberration correction and monochromation, allowing studies of chemical reactions and growth processes with improved spatial and spectral resolution. These additions to the columns of commercial ETEMs have...... are confined to a thin (typically 50-200 μm thick) slab around the sample, but the electrons interact with the window material (e.g. C, SiN) as well as with the gas and the sample. In addition, the field of view is typically smaller than in a conventional TEM and a limited range of sample geometries can...

  8. From spin flip excitations to the spin susceptibility enhancement of a two-dimensional electron gas.

    Science.gov (United States)

    Perez, F; Aku-leh, C; Richards, D; Jusserand, B; Smith, L C; Wolverson, D; Karczewski, G

    2007-07-13

    The g-factor enhancement of the spin-polarized two-dimensional electron gas was measured directly over a wide range of spin polarizations, using spin flip resonant Raman scattering spectroscopy on two-dimensional electron gases embedded in Cd(1-x)Mn(x)Te semimagnetic quantum wells. At zero Raman transferred momentum, the single-particle spin flip excitation, energy Z*, coexists in the Raman spectrum with the spin flip wave of energy Z, the bare giant Zeeman splitting. We compare the measured g-factor enhancement with recent spin-susceptibility enhancement theories and deduce the spin-polarization dependence of the mass renormalization.

  9. Alloy-disorder scattering in the quasi-one dimensional electron gas

    Science.gov (United States)

    Gold, A.; Ghazali, A.

    1992-08-01

    We calculate the mobility μ due to alloy-disorder scattering in a quasi-one-dimensional electron gas. In the one-subband approximation the screening effects are taken into account. We discuss the dependence of μ on the wire radius and the electron density and derive analytical results. We compare our results with the mobility due to interface-roughness scattering and conclude that in In 0.53Ga 0.47As/InP wires alloy-disorder scattering is more important than interface-roughness scattering. Our results should apply to recently realized In 0.53Ga 0.47As/InP wires.

  10. New nonlinear structures in a degenerate one-dimensional electron gas

    CERN Document Server

    Ghosh, S; Haas, F

    2014-01-01

    The collective dynamics of nonlinear electron waves in an one-dimensional degenerate electron gas is treated using the Lagrangian fluid approach. A new class of solutions with a nontrivial space and time dependence is derived. Both analytical and numerical results demonstrate the formation of stable, breather-like modes, provided certain conditions are meet. For large amplitude of the initial density perturbation, a catastrophic collapse of the plasma density is predicted, even in the presence of the quantum statistical pressure and quantum diffraction dispersive effects. The results are useful for the understanding of the properties of general nonlinear structures in dense plasmas.

  11. Hierarchical graphene-polyaniline nanocomposite films for high-performance flexible electronic gas sensors

    Science.gov (United States)

    Guo, Yunlong; Wang, Ting; Chen, Fanhong; Sun, Xiaoming; Li, Xiaofeng; Yu, Zhongzhen; Wan, Pengbo; Chen, Xiaodong

    2016-06-01

    A hierarchically nanostructured graphene-polyaniline composite film is developed and assembled for a flexible, transparent electronic gas sensor to be integrated into wearable and foldable electronic devices. The hierarchical nanocomposite film is obtained via aniline polymerization in reduced graphene oxide (rGO) solution and simultaneous deposition on flexible PET substrate. The PANI nanoparticles (PPANI) anchored onto rGO surfaces (PPANI/rGO) and the PANI nanofiber (FPANI) are successfully interconnected and deposited onto flexible PET substrates to form hierarchical nanocomposite (PPANI/rGO-FPANI) network films. The assembled flexible, transparent electronic gas sensor exhibits high sensing performance towards NH3 gas concentrations ranging from 100 ppb to 100 ppm, reliable transparency (90.3% at 550 nm) for the PPANI/rGO-FPANI film (6 h sample), fast response/recovery time (36 s/18 s), and robust flexibility without an obvious performance decrease after 1000 bending/extending cycles. The excellent sensing performance could probably be ascribed to the synergetic effects and the relatively high surface area (47.896 m2 g-1) of the PPANI/rGO-FPANI network films, the efficient artificial neural network sensing channels, and the effectively exposed active surfaces. It is expected to hold great promise for developing flexible, cost-effective, and highly sensitive electronic sensors with real-time analysis to be potentially integrated into wearable flexible electronics.A hierarchically nanostructured graphene-polyaniline composite film is developed and assembled for a flexible, transparent electronic gas sensor to be integrated into wearable and foldable electronic devices. The hierarchical nanocomposite film is obtained via aniline polymerization in reduced graphene oxide (rGO) solution and simultaneous deposition on flexible PET substrate. The PANI nanoparticles (PPANI) anchored onto rGO surfaces (PPANI/rGO) and the PANI nanofiber (FPANI) are successfully

  12. Free Energy of the Uniform Electron Gas: Testing Analytical Models against First Principle Results

    CERN Document Server

    Groth, Simon; Bonitz, Michael

    2016-01-01

    The uniform electron gas is a key model system in the description of matter, including dense plasmas and solid state systems. However, the simultaneous occurence of quantum, correlation, and thermal effects makes the theoretical description challenging. For these reasons, over the last half century many analytical approaches have been developed the accuracy of which has remained unclear. We have recently obtained the first \\textit{ab initio} data for the exchange correlation free energy of the uniform electron gas [T. Dornheim \\textit{et al.}, Phys.~Rev.~Lett.~\\textbf{117}, 156403 (2016)] which now provides the opportunity to assess the quality of the mentioned approaches and parametrizations. Particular emphasis is put on the warm dense matter regime, where we find significant discrepancies between the different approaches.

  13. Anisotropic Heisenberg form of RKKY interaction in the one-dimensional spin-polarized electron gas

    Science.gov (United States)

    Valizadeh, M. M.

    2016-09-01

    We study the indirect exchange interaction between two localized magnetic moments, known as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, in a one-dimensional (1D) spin-polarized electron gas. We find explicit expressions for each term of this interaction, study their oscillatory behaviors as a function of the distance between two magnetic moments, R, and compare them with the known results for RKKY interaction in the case of 1D standard electron gas. We show this interaction can be written in an anisotropic Heisenberg form, E(R) = λ2χ xx(S1xS2x + S1yS2y) + λ2χ zzS1zS2z, coming from broken time-reversal symmetry of the host material.

  14. Properties of two-dimensional electron gas containing self-organized quantum antidots

    Science.gov (United States)

    Vasilyev, Yu.; Suchalkin, S.; Zundel, M.; Heisenberg, D.; Eberl, K.; von Klitzing, K.

    1999-11-01

    A nonuniform two-dimensional electron gas in a heterojunction with inserted self-organized electrically inactive dots (acting as antidots) has been fabricated by molecular-beam epitaxy of AlGaAs/AlInAs/GaAs layer sequences. Transport measurements give the ratio of the transport mobility to the quantum mobility less than four, which suggests that the dominant scattering at low magnetic fields is the short-range scattering from the lateral potential of the antidots. Far-infrared cyclotron resonance (CR) spectra show an absorption mode as narrow as 0.5 cm-1 at high magnetic fields associated with the high-mobility electron gas formed between the antidot islands and confined in the lateral directions. The confinement energy of 14 cm-1 is derived from the CR spectra.

  15. Piecewise parabolic negative magnetoresistance of two-dimensional electron gas with triangular antidot lattice

    Energy Technology Data Exchange (ETDEWEB)

    Budantsev, M. V., E-mail: budants@isp.nsc.ru; Lavrov, R. A.; Pogosov, A. G.; Zhdanov, E. Yu.; Pokhabov, D. A. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2011-02-15

    Extraordinary piecewise parabolic behavior of the magnetoresistance has been experimentally detected in the two-dimensional electron gas with a dense triangular lattice of antidots, where commensurability magnetoresistance oscillations are suppressed. The magnetic field range of 0-0.6 T can be divided into three wide regions, in each of which the magnetoresistance is described by parabolic dependences with high accuracy (comparable to the experimental accuracy) and the transition regions between adjacent regions are much narrower than the regions themselves. In the region corresponding to the weakest magnetic fields, the parabolic behavior becomes almost linear. The observed behavior is reproducible as the electron gas density changes, which results in a change in the resistance by more than an order of magnitude. Possible physical mechanisms responsible for the observed behavior, including so-called 'memory effects,' are discussed.

  16. Communication: Simple and accurate uniform electron gas correlation energy for the full range of densities

    Science.gov (United States)

    Chachiyo, Teepanis

    2016-07-01

    A simple correlation energy functional for the uniform electron gas is derived based on the second-order Moller-Plesset perturbation theory. It can reproduce the known correlation functional in the high-density limit, while in the mid-density range maintaining a good agreement with the near-exact correlation energy of the uniform electron gas to within 2 × 10-3 hartree. The correlation energy is a function of a density parameter rs and is of the form a * ln ( 1 + /b r s + /b rs 2 ) . The constants "a" and "b" are derived from the known correlation functional in the high-density limit. Comparisons to the Ceperley-Alder's near-exact Quantum Monte Carlo results and the Vosko-Wilk-Nusair correlation functional are also reported.

  17. Electronic properties of NH4-adsorbed graphene nanoribbon as a promising candidate for a gas sensor

    Directory of Open Access Journals (Sweden)

    Naoki Harada

    2016-05-01

    Full Text Available The electronic properties of NH4-adsorbed N = 7 armchair graphene nanoribbons (AGNRs were theoretically investigated using self-consistent atomistic simulations to explore the feasibility of AGNRs as a gas sensing material. Whereas a pristine AGNR has a finite band gap and is an intrinsic semiconductor, an NH4-adsorbed AGNR exhibits heavily doped n-type properties similar to a graphene sheet with the molecules adsorbed. The electric characteristics of a back-gated AGNR gas sensor were also simulated and the drain current changed exponentially with increasing number of adsorbed molecules. We may conclude that an AGNR is promising as a highly sensitive gas-sensing material with large outputs.

  18. Equation of state of the relativistic free electron gas at arbitrary degeneracy

    Science.gov (United States)

    Faussurier, Gérald

    2016-12-01

    We study the problem of the relativistic free electron gas at arbitrary degeneracy. The specific heat at constant volume and particle number CV and the specific heat at constant pressure and particle number CP are calculated. The question of equation of state is also studied. Non degenerate and degenerate limits are considered. We generalize the formulas obtained in the non-relativistic and ultra-relativistic regimes.

  19. Silver ionic and electronic conductivity in Ag9GaS6

    NARCIS (Netherlands)

    Hellstrom, E.E.; Schoonman, J.

    1980-01-01

    Electrical measurements on the mixed ionic, electronic conductor Ag9GaS6, which undergoes a phase transition at 303 K, were performed. The silver ionic conductivity in the low-temperature α-form measured using an ionic 4-probe method, is given by σT = 4.3 × 106 exp [(-29.8kJ/mol)/ RT] S m-1 K. The e

  20. Magnetoresistance of a two-dimensional electron gas in a random magnetic field

    DEFF Research Database (Denmark)

    Smith, Anders; Taboryski, Rafael Jozef; Hansen, Luise Theil

    1994-01-01

    We report magnetoresistance measurements on a two-dimensional electron gas made from a high-mobility GaAs/AlxGa1-xAs heterostructure, where the externally applied magnetic field was expelled from regions of the semiconductor by means of superconducting lead grains randomly distributed on the surf...... on the surface of the sample. A theoretical explanation in excellent agreement with the experiment is given within the framework of the semiclassical Boltzmann equation. © 1994 The American Physical Society...

  1. Plasmon spectrum of degenerated electron gas. T=0 Green function method. Detailed pedagogical derivation

    OpenAIRE

    Mishonov, Todor M.; Atanasova, Liliya A.; Ivanov, Peter A; Valchev, Tihomir I.; Arnaudov, Dimo L.

    2003-01-01

    Plasmon spectrum and polarization operator of 1, 2, and 3 dimensional electron gas are calculated by T=0 Green function technique. It is shown that this field theory method gives probably the simplest pedagogical derivation of the statistical problem for the response function. The explanation is complimentary to the standard courses on condensed matter and plasma physics of the level of IX volume of Landau-Lifshitz encyclopedia on theoretical physics.

  2. Interaction-induced huge magnetoresistance in a high mobility two-dimensional electron gas

    Energy Technology Data Exchange (ETDEWEB)

    Bockhorn, L.; Haug, R. J. [Institut für Festkörperphysik, Leibniz Universität Hannover, D-30167 Hannover (Germany); Gornyi, I. V. [Institut für Nanotechnologie, Karlsruher Institut of Technology, D-76021 Karlsruhe (Germany); Schuh, D. [Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93053 Regensburg (Germany); Wegscheider, W. [ETH Zürich (Switzerland)

    2013-12-04

    A strong negative magnetoresistance is observed in a high-mobility two-dimensional electron gas in a GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum well. We discuss that the negative magnetoresistance consists of a small peak induced by a combination of two types of disorder and a huge magnetoresistance explained by the interaction correction to the conductivity for mixed disorder.

  3. CYP2D6 polymorphism in relation to tramadol metabolism

    DEFF Research Database (Denmark)

    Halling, Jónrit; Weihe, Pál; Brosen, Kim

    2008-01-01

    Several studies have demonstrated the impact of CYP2D6 polymorphism on the pharmacokinetics of tramadol. However, the relationship between the O-demethylation of tramadol and O-desmethyltramadol (M1) and CYP2D6 activity has not previously been investigated with tramadol in multimedicated...... outpatients under steady-state conditions. Hence, the aim of this study was to determine if the well documented pharmacokinetics of tramadol regarding CYP2D6 could be verified in a study including 88 multimedicated Faroese patients, treated with tramadol at steady-state conditions. Further, the study aimed...... collection over 12 hours. Sparteine and its metabolites were assayed by gas chromatography. Genotype analyses for the CYP2D6 3, 4, 6, and 9 alleles were performed by polymerase chain reaction and Taqman technology. Plasma and urinary concentrations of (+/-)-tramadol and (+/-)-M1 were determined by high...

  4. Master curves for gas amplification in low vacuum and environmental scanning electron microscopy.

    Science.gov (United States)

    Thiel, Bradley L

    2004-02-01

    The concept of universal amplification profiles for gas cascade amplification of signals in low vacuum and environmental scanning electron microscopes is demonstrated both experimentally and theoretically using water vapor. For a given gas, cascade amplification gain profiles can be plotted onto a single master curve where the independent reduced parameter is the ratio of pressure to amplification field strength. When plotted in this fashion, both desired secondary electron and spurious background signal components fall onto respective master curves, with the amplitude being a function of anode bias only. These master curves can be described by simple Townsend Gas Capacitor equations using only two gas-specific parameters. As long as single scattering conditions apply, this approach allows for simplified, direct comparison of the gain characteristics of different gases and allows more intelligent selection of imaging conditions. The utility of treating signal amplification in this manner is demonstrated through a series of images collected under a variety of conditions, but with the ratio of pressure to amplification field strength kept constant. In practice, the range of operational parameter space in which this description can be applied to imaging is limited, as images typically have a mixture of secondary and backscattered contributions.

  5. Direct Imaging of Charge Density Modulation in Switchable Two-Dimensional Electron Gas at the Oxide Hetero-Interfaces by Using Electron Bean Inline Holography

    Science.gov (United States)

    2015-08-16

    SUPPLEMENTARY NOTES 14. ABSTRACT The recent discovery of a two-dimensional electron gas (2DEG) at the interface between insulating perovskite ...3/10/2015 Abstract The recent discovery of a two-dimensional electron gas (2DEG) at the interface between insulating perovskite oxides SrTiO3...associated charge distributions in semiconductor materials, and therefore regarded as the only tool that can completely visualize the spatial

  6. Experiences with a pre-series of Micro Strip Gas Counters with Gas Electron Multipliers for high rate applications

    CERN Document Server

    Zander, Anette

    2001-01-01

    Micro strip gas chambers (MSGCs) are promising candidates for large scale applications. They combine a good spatial resolution with high granularity and low cost. As a possible extension of the plain MSGC, a Gas Electron Multiplier (GEM) foil may be implemented into the detector in order to increase the safety of operation. It was planned to equip the outer part of the tracking system of the Compact Muon Solenoid (CMS) experiment at the future Large Hadron Collider (LHC) at the Centre de Recherche Nucleaire (CERN) with MSGCs. In the barrel part of the tracker, plain MSGCs were to be used. For the forward part, the MSGC+GEM technology was envisaged. This thesis describes the assembly and test of a pre-series of 18 fully functional MSGC+GEM forward detector modules to determine their radiation hardness and their readiness for mass production. Five of the modules were built at Aachen, thirteen more at the 'Institut für Experimentelle Kernphysik' in Karlsruhe. For the pre-series, two different types of GEM foils...

  7. The Analytical Approximate Solution of the 2D Thermal Displacement

    Institute of Scientific and Technical Information of China (English)

    Chu-QuanGuan; Zeng-YuanGuo; 等

    1996-01-01

    The 2D plane gas flow under heating (with nonentity boundary condition)has been discussed by the analytical approach in this paper.The approximate analytical solutions have been obtained for the flow passing various kinds of heat sources.Solutions demonstrate the thermal displacement phenomena are strongly depend on the heating intensity.

  8. Double ionization effect in electron accelerations by high-intensity laser pulse interaction with a neutral gas

    Science.gov (United States)

    Nandan Gupta, Devki

    2013-11-01

    We study the effect of laser-induced double-ionization of a helium gas (with inhomogeneous density profile) on vacuum electron acceleration. For enough laser intensity, helium gas can be found doubly ionized and it strengthens the divergence of the pulse. The double ionization of helium gas can defocus the laser pulse significantly, and electrons are accelerated by the front of the laser pulse in vacuum and then decelerated by the defocused trail part of the laser pulse. It is observed that the electrons experience a very low laser-intensity at the trailing part of the laser pulse. Hence, there is not much electron deceleration at the trailing part of the pulse. We found that the inhomogeneity of the neutral gas reduced the rate of tunnel ionization causing less defocusing of the laser pulse and thus the electron energy gain is reduced.

  9. Double ionization effect in electron accelerations by high-intensity laser pulse interaction with a neutral gas

    Directory of Open Access Journals (Sweden)

    Gupta Devki Nandan

    2013-11-01

    Full Text Available We study the effect of laser-induced double-ionization of a helium gas (with inhomogeneous density profile on vacuum electron acceleration. For enough laser intensity, helium gas can be found doubly ionized and it strengthens the divergence of the pulse. The double ionization of helium gas can defocus the laser pulse significantly, and electrons are accelerated by the front of the laser pulse in vacuum and then decelerated by the defocused trail part of the laser pulse. It is observed that the electrons experience a very low laser-intensity at the trailing part of the laser pulse. Hence, there is not much electron deceleration at the trailing part of the pulse. We found that the inhomogeneity of the neutral gas reduced the rate of tunnel ionization causing less defocusing of the laser pulse and thus the electron energy gain is reduced.

  10. Computational studies of suppression of microwave gas breakdown by crossed dc magnetic field using electron fluid model

    Science.gov (United States)

    Zhao, Pengcheng; Guo, Lixin; Shu, Panpan

    2016-08-01

    The gas breakdown induced by a square microwave pulse with a crossed dc magnetic field is investigated using the electron fluid model, in which the accurate electron energy distribution functions are adopted. Simulation results show that at low gas pressures the dc magnetic field of a few tenths of a tesla can prolong the breakdown formation time by reducing the mean electron energy. With the gas pressure increasing, the higher dc magnetic field is required to suppress the microwave breakdown. The electric field along the microwave propagation direction generated due to the motion of electrons obviously increases with the dc magnetic field, but it is much less than the incident electric field. The breakdown predictions of the electron fluid model agree very well with the particle-in-cell-Monte Carlo collision simulations as well as the scaling law for the microwave gas breakdown.

  11. Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

    Indian Academy of Sciences (India)

    P K Ghosh; A Ghosal; D Chattopadhyay

    2009-02-01

    Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

  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; Deux systemes d'electrons fortement correles: le modele de reseau Kondo dans la limite du couplage fort et un modele bidimensionnel d'electrons au voisinage d'une transition topologique electronique

    Energy Technology Data Exchange (ETDEWEB)

    Bouis, F

    1999-10-14

    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. Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes

    Science.gov (United States)

    Miyamoto, Akihito; Lee, Sungwon; Cooray, Nawalage Florence; Lee, Sunghoon; Mori, Mami; Matsuhisa, Naoji; Jin, Hanbit; Yoda, Leona; Yokota, Tomoyuki; Itoh, Akira; Sekino, Masaki; Kawasaki, Hiroshi; Ebihara, Tamotsu; Amagai, Masayuki; Someya, Takao

    2017-09-01

    Thin-film electronic devices can be integrated with skin for health monitoring and/or for interfacing with machines. Minimal invasiveness is highly desirable when applying wearable electronics directly onto human skin. However, manufacturing such on-skin electronics on planar substrates results in limited gas permeability. Therefore, it is necessary to systematically investigate their long-term physiological and psychological effects. As a demonstration of substrate-free electronics, here we show the successful fabrication of inflammation-free, highly gas-permeable, ultrathin, lightweight and stretchable sensors that can be directly laminated onto human skin for long periods of time, realized with a conductive nanomesh structure. A one-week skin patch test revealed that the risk of inflammation caused by on-skin sensors can be significantly suppressed by using the nanomesh sensors. Furthermore, a wireless system that can detect touch, temperature and pressure is successfully demonstrated using a nanomesh with excellent mechanical durability. In addition, electromyogram recordings were successfully taken with minimal discomfort to the user.

  14. Study of spatial resolution of coordinate detectors based on Gas Electron Multipliers

    Science.gov (United States)

    Kudryavtsev, V. N.; Maltsev, T. V.; Shekhtman, L. I.

    2017-02-01

    Spatial resolution of GEM-based tracking detectors is determined in the simulation and measured in the experiments. The simulation includes GEANT4 implemented transport of high energy electrons with careful accounting of atomic relaxation processes including emission of fluorescent photons and Auger electrons and custom post-processing with accounting of diffusion, gas amplification fluctuations, distribution of signals on readout electrodes, electronics noise and particular algorithm of final coordinate calculation (center of gravity). The simulation demonstrates that the minimum of spatial resolution of about 10 μm can be achieved with a gas mixture of Ar -CO2 (75-25 %) at a strips pitch from 250 μm to 300 μm. At a larger pitch the resolution quickly degrades reaching 80-100 μm at a pitch of 460-500 μm. Spatial resolution of low-material triple-GEM detectors for the DEUTERON facility at the VEPP-3 storage ring is measured at the extracted beam facility of the VEPP-4 M collider. One-coordinate resolution of the DEUTERON detector is measured with electron beam of 500 MeV, 1 GeV and 3.5 GeV energies. The determined value of spatial resolution varies in the range from approximately 35 μm to 50 μm for orthogonal tracks in the experiments.

  15. Density of states in a two-dimensional electron gas: Impurity bands and band tails

    Science.gov (United States)

    Gold, A.; Serre, J.; Ghazali, A.

    1988-03-01

    We calculate the density of states of a two-dimensional electron gas in the presence of charged impurities within Klauder's best multiple-scattering approach. The silicon metal-oxide-semiconductor (MOS) system with impurities at the interface is studied in detail. The finite extension of the electron wave function into the bulk is included as well as various dependences of the density of states on the electron, the depletion, and the impurity densities. The transition from an impurity band at low impurity concentration to a band tail at high impurity concentration is found to take place at a certain impurity concentration. If the screening parameter of the electron gas is decreased, the impurity band shifts to lower energy. For low impurity density we find excited impurity bands. Our theory at least qualitatively explains conductivity and infrared-absorption experiments on impurity bands in sodium-doped MOS systems and deep band tails in the gap observed for high doping levels in these systems.

  16. Determination of phenoxy acid herbicides in water by electron-capture and microcoulometric gas chromatography

    Science.gov (United States)

    Goerlitz, D.F.; Lamar, William L.

    1967-01-01

    A sensitive gas chromatographic method using microcoulometric titration and electron-capture detection for the analysis of 2,4-D, silvex, 2,4,5-T, and other phenoxy acid herbicides in water is described. The herbicides are extracted from unfiltered water samples (800-1,000 ml) by use of ethyl ether ; then the herbicides are concentrated and esterilied. To allow the analyst a choice, two esterilication procedures--using either boron trifluoride-methanol or diazomethane--are evaluated. Microcoulometric gas chromatography is specific for the detection of halogenated compounds such as the phenoxy acid herbicides whereas it does not respond to nonhalogenated components. Microcoulometric gas chromatography requires care and patience. It is not convenient for rapid screening of l-liter samples that contain less than 1 microgram of the herbicide. Although electroncapture gas chromatography is less selective and more critically affected by interfering substances, it is, nevertheless, convenient and more sensitive than microcoulometric gas chromatography. Two different liquid phases are used in the gas chromatographic columns--DC-200 silicone in one column and QF-1 silicone in the other. The performance of both columns is improved by the addition of Carbowax 20M. The Gas Chrom Q support is coated with the liquid phases by the 'frontal-analysis' technique. The practical lower limits for measurement of the phenoxy acid herbicides in water primarily depend upon the sample size, interferences present, anal instrumentation used. With l-liter samples of water, the practical lower limits of measurement are 10 ppt (parts per trillion) for 2,4-D and 2 ppt for silvex and 2,4,5-T when electron-capture detection is used, and approximately 20 ppt for each herbicide when analyzed by microcoulometric-titration gas chromatography. Recoveries of the herbicides immediately after addition to unfiltered water samples averaged 92 percent for 2,4-D, 90 percent for silvex, and 98 percent for 2

  17. Realization and Characterization of a Curved Two-dimensional Electron Gas

    Science.gov (United States)

    Shaji, Nakul; Deneke, Christoph

    2005-03-01

    Using the built-in strain from lattice mismatch between Al0.33Ga0.67As and In0.2Ga0.8As as a bending force, a strip of two-dimensional electron gas (2DEG) in an AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructure is curved into a tube when released from the substrate by wet etching. A variety of mesoscopic quantum devices can be defined in such curved 2DEG structures. This technology opens the door for investigating geometry-dependent electron transport under non-uniform magnetic fields. We have defined Hall bar patterns from a sheet of 2DEG using both optical and electron-beam lithography. The sample characterization under an external magnetic field will be discussed.

  18. Brightness measurement of an electron impact gas ion source for proton beam writing applications

    Energy Technology Data Exchange (ETDEWEB)

    Liu, N.; Santhana Raman, P. [Centre for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore); Xu, X.; Pang, R.; Kan, J. A. van, E-mail: phyjavk@nus.edu.sg [Centre for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542 (Singapore); Khursheed, A. [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore)

    2016-02-15

    We are developing a high brightness nano-aperture electron impact gas ion source, which can create ion beams from a miniature ionization chamber with relatively small virtual source sizes, typically around 100 nm. A prototype source of this kind was designed and successively micro-fabricated using integrated circuit technology. Experiments to measure source brightness were performed inside a field emission scanning electron microscope. The total output current was measured to be between 200 and 300 pA. The highest estimated reduced brightness was found to be comparable to the injecting focused electron beam reduced brightness. This translates into an ion reduced brightness that is significantly better than that of conventional radio frequency ion sources, currently used in single-ended MeV accelerators.

  19. Photo-fragmentation and electron-detachment studies of gas-phase chromophore ions

    DEFF Research Database (Denmark)

    Rahbek, Dennis Bo

    -physical properties of two important bio-chromophores by investigating the properties of structural isomers of these molecules. The chromophores are the ones found in the green fluorescent protein and the photoactive yellow protein. The photo-physical properties have been studied experimentally in the gas phase...... excitation energy. This results in a competition between de-excitation by internal conversion and electron emission. Both of these processes are of non-adiabatic character as they rely on coupling between electronic energy and energy in nuclear motion. Moreover, it is found that higher-lying states...... in the anionic forms serves as ‘doorway’- states into the continuum of the neutral radical. Regarding the structural isomeric forms of each of the chromophores we find that the degree of electronic coupling between the subunitsmaking up the chromophores is crucial for the tuning the absorption properties, both...

  20. Many-body aspects of positron annihilation in the electron gas

    Science.gov (United States)

    Apaja, V.; Denk, S.; Krotscheck, E.

    2003-11-01

    We investigate positron annihilation in the electron gas as a case study for many-body theory, in particular, the Fermi-hypernetted-chain Euler-Lagrange (FHNC-EL) method. We examine several approximation schemes and show that one has to go up to the most sophisticated implementation of the theory available at the moment in order to get annihilation rates that agree reasonably well with experimental data. Even though there is basically just one number we look at, namely, the electron-positron pair-distribution function at zero distance, it is exactly this number that dictates how the full pair distribution behaves: in most cases, it falls off monotonously towards unity as the distance increases. Cases where the electron-positron pair distribution exhibits a dip are precursors to the formation of bound electron-positron pairs. The formation of electron-positron pairs is indicated by a divergence of the FHNC-EL equations; from this we can estimate the density regime where positrons must be localized. This occurs in our calculations in the range 9.4⩽rs⩽10, where rs is the dimensionless density parameter of the electron liquid.

  1. Simulation and experimental results for the detection of conversion electrons with gas proportional scintillation counters

    CERN Document Server

    Rachinhas, P J B M; Lopes, J A M; Dias, T; Morgado, R E; Santos, J M; Stauffer, A D; Conde, C A N

    2000-01-01

    The application of gas proportional scintillation counters (GPSC) to the detection and identification of conversion electrons in the medium energy range is investigated. Experimental and Monte Carlo results are presented for the response of a xenon GPSC, filled at atmospheric pressure, to the decay of a sup 1 sup 0 sup 9 Cd source. This source emits 88.0 keV gamma-rays, e sub L =84.6 keV and e sub K =62.5 keV conversion electrons, as well as fluorescence X-rays and Auger electrons. Good agreement is found between the measured and the calculated energy spectra. The response to higher-energy electrons is investigated by Monte Carlo simulation, by considering a hypothetical GPSC filled with xenon at 10 atm and doped with the sup 1 sup 3 sup 3 sup m Xe metastable isotope. The calculated energy spectra for the absorption of the sup 1 sup 3 sup 3 sup m Xe 233.2 keV gamma-rays, e sub K =198.6 keV and e sub L =228.4 keV conversion electrons, as well as fluorescence X-rays and Auger electrons, are presented and discus...

  2. 2D fluid simulations of interchange turbulence with ion dynamics

    DEFF Research Database (Denmark)

    Nielsen, Anders Henry; Madsen, Jens; Xu, G. S.

    2013-01-01

    In this paper we present a first principle global two-dimensional fluid model. The HESEL (Hot Edge SOL Electrostatic) model is a 2D numerical fluid code, based on interchange dynamics and includes besides electron also the ion pressure dynamic. In the limit of cold ions the model almost reduces......B vorticity as well as the ion diamagnetic vorticity. The 2D domain includes both open and closed field lines and is located on the out-board midplane of a tokamak. On open field field lines the parallel dynamics are parametrized as sink terms depending on the dynamic quantities; density, electron and ion...

  3. 2D metal carbides and nitrides (MXenes) for energy storage

    Science.gov (United States)

    Anasori, Babak; Lukatskaya, Maria R.; Gogotsi, Yury

    2017-01-01

    The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research.

  4. 2D metal carbides and nitrides (MXenes) for energy storage

    KAUST Repository

    Anasori, Babak

    2017-01-17

    The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research.

  5. Learn Unity for 2D game development

    CERN Document Server

    Thorn, Alan

    2013-01-01

    The only Unity book specifically covering 2D game development Written by Alan Thorn, experience game developer and author of seven books on game programming Hands-on examples of all major aspects of 2D game development using Unity

  6. Emerging and potential opportunities for 2D flexible nanoelectronics

    Science.gov (United States)

    Zhu, Weinan; Park, Saungeun; Akinwande, Deji

    2016-05-01

    The last 10 years have seen the emergence of two-dimensional (2D) nanomaterials such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP) among the growing portfolio of layered van der Waals thin films. Graphene, the prototypical 2D material has advanced rapidly in device, circuit and system studies that has resulted in commercial large-area applications. In this work, we provide a perspective of the emerging and potential translational applications of 2D materials including semiconductors, semimetals, and insulators that comprise the basic material set for diverse nanosystems. Applications include RF transceivers, smart systems, the so-called internet of things, and neurotechnology. We will review the DC and RF electronic performance of graphene and BP thin film transistors. 2D materials at sub-um channel length have so far enabled cut-off frequencies from baseband to 100GHz suitable for low-power RF and sub-THz concepts.

  7. Nitrogen as a carrier gas for regime control in focused electron beam induced deposition

    Directory of Open Access Journals (Sweden)

    Wachter Stefan

    2014-01-01

    Full Text Available This work reports on focused electron beam induced deposition (FEBID using a custom built gas injection system (GIS equipped with nitrogen as a gas carrier. We have deposited cobalt from Co2(CO8, which is usually achieved by a heated GIS. In contrast to a heated GIS, our strategy allows avoiding problems caused by eventual temperature gradients along the GIS. Moreover, the use of the gas carrier enables a high control over process conditions and consequently the properties of the synthesized nanostructures. Chemical composition and growth rate are investigated by energy dispersive X-ray spectroscopy (EDX and atomic force microscopy (AFM, respectively. We demonstrate that the N2 flux is strongly affecting the deposit growth rate without the need of heating the precursor in order to increase its vapour pressure. Particularly, AFM volume estimation of the deposited structures showed that increasing the nitrogen resulted in an enhanced deposition rate. The wide range of achievable precursor fluxes allowed to clearly distinguish between precursor- and electron-limited regime. With the carrier-based GIS an optimized deposition procedure with regards to the desired deposition regime has been enabled

  8. Polymer ultrapermeability from the inefficient packing of 2D chains

    Science.gov (United States)

    Rose, Ian; Bezzu, C. Grazia; Carta, Mariolino; Comesaña-Gándara, Bibiana; Lasseuguette, Elsa; Ferrari, M. Chiara; Bernardo, Paola; Clarizia, Gabriele; Fuoco, Alessio; Jansen, Johannes C.; Hart, Kyle E.; Liyana-Arachchi, Thilanga P.; Colina, Coray M.; McKeown, Neil B.

    2017-09-01

    The promise of ultrapermeable polymers, such as poly(trimethylsilylpropyne) (PTMSP), for reducing the size and increasing the efficiency of membranes for gas separations remains unfulfilled due to their poor selectivity. We report an ultrapermeable polymer of intrinsic microporosity (PIM-TMN-Trip) that is substantially more selective than PTMSP. From molecular simulations and experimental measurement we find that the inefficient packing of the two-dimensional (2D) chains of PIM-TMN-Trip generates a high concentration of both small (carbon capture demonstrated for relevant gas mixtures. Comparisons between PIM-TMN-Trip and structurally similar polymers with three-dimensional (3D) contorted chains confirm that its additional intrinsic microporosity is generated from the awkward packing of its 2D polymer chains in a 3D amorphous solid. This strategy of shape-directed packing of chains of microporous polymers may be applied to other rigid polymers for gas separations.

  9. Development of gas pulsing system for electron cyclotron resonance ion sourcea)

    Science.gov (United States)

    Hojo, S.; Honma, T.; Muramatsu, M.; Sakamoto, Y.; Sugiura, A.

    2008-02-01

    A gas-pulsing system for an electron cyclotron resonance ion source with all permanent magnets (Kei2 source) at NIRS has been developed and tested. The system consists of a small vessel (30ml) to reserve CH4 gas and two fast solenoid valves that are installed at both sides of the vessel. They are connected to each other and to the Kei2 source by using a stainless-steel pipe (4mm inner diameter), where the length of the pipe from the valve to the source is 60cm and the conductance is 1.2l /s. From the results of the test, almost 300eμA for a pulsed C4+12 beam was obtained at a Faraday cup in an extraction-beam channel with a pressure range of 4000Pa in the vessel. At this time, the valve has an open time of 10ms and the delay time between the valve open time and the application of microwave power is 100ms. In experiments, the conversion efficiency for input CH4 molecules to the quantity of extracted C4+12 ions in one beam pulse was found to be around 3% and the ratio of the total amount of the gas requirement was only 10% compared with the case of continuous gas provided in 3.3s of repetition in HIMAC.

  10. An improved measurement of electron-ion recombination in high-pressure xenon gas

    CERN Document Server

    Serra, L; Álvarez, V; Borges, F I G; Camargo, M; Cárcel, S; Cebrián, S; Cervera, A; Conde, C A N; Dafni, T; Díaz, J; Esteve, R; Fernandes, L M P; Ferrario, P; Ferreira, A L; Freitas, E D C; Gehman, V M; Goldschmidt, A; Gómez-Cadenas, J J; González-Díaz, D; Gutiérrez, R M; Hauptman, J; Morata, J A Hernando; Herrera, D C; Irastorza, I G; Labarga, L; Laing, A; Liubarsky, I; Lopez-March, N; Lorca, D; Losada, M; Luzón, G; Marí, A; Martín-Albo, J; Martínez-Lema, G; Martínez, A; Miller, T; Monrabal, F; Monserrate, M; Monteiro, C M B; Mora, F J; Moutinho, L M; Vidal, J Muñoz; Nebot-Guinot, M; Nygren, D; Oliveira, C A B; Pérez, J; Aparicio, J L Pérez; Querol, M; Renner, J; Ripoll, L; Rodríguez, A; Rodríguez, J; Santos, F P; Santos, J M F dos; Shuman, D; Simón, A; Sofka, C; Toledo, J F; Torrent, J; Tsamalaidze, Z; Veloso, J F C A; Villar, J A; Webb, R; White, J T; Yahlali, N

    2014-01-01

    We report on results obtained with the NEXT-DEMO prototype of the NEXT-100 high-pressure xenon gas time projection chamber (TPC), exposed to an alpha decay calibration source. Compared to our previous measurements with alpha particles, an upgraded detector and improved analysis techniques have been used. We measure event-by-event correlated fluctuations between ionization and scintillation due to electron-ion recombination in the gas, with correlation coeffcients between -0.80 and -0.56 depending on the drift field conditions. By combining the two signals, we obtain a 2.8 % FWHM energy resolution for 5.49 MeV alpha particles and a measurement of the optical gain of the electroluminescent TPC. The improved energy resolution also allows us to measure the specific activity of the radon in the gas due to natural impurities. Finally, we measure the average ratio of excited to ionized atoms produced in the xenon gas by alpha particles to be $0.561\\pm 0.045$, translating into an average energy to produce a primary s...

  11. Feasibility Study of Gas Electron Multiplier Detector as an X-Ray Image Sensor

    CERN Document Server

    Shin, Sukyoung; Lee, Soonhyouk

    2015-01-01

    For its ease manufacturing, flexible geometry, and cheap manufacturing cost, the gas electron multiplier (GEM) detector can be used as an x-ray image sensor. For this purpose, we acquired relative detection efficiencies and suggested a method to increase the detection efficiency in order to study the possibility of GEM detector as an x-ray image sensor. The GEM detector system is composed of GEM foils, the instrument system, the gas system, and the negative power supply. The instrument system consists of the A225 charge sensitive preamp, A206 discriminator, and MCA8000D multichannel analyzer. For the gas system, Argon gas was mixed with CO2 to the ratio of 8:2, and for the negative 2,000 volts, the 3106D power supply was used. The CsI-coated GEM foil was used to increase the detection efficiency. Fe-55 was used as an x-ray source and the relative efficiency was acquired by using the ratio of GEM detector to the CdTe detector. The total count method and the energy spectrum method were used to calculate the rel...

  12. Liquid-like 2D plasmonic waves (Conference Presentation)

    Science.gov (United States)

    Zhang, Baile

    2017-05-01

    We predict some novel 2D plasmonic waves as analogues of corresponding hydrodynamic wave phenomena, including plasmonic splashing and V-shaped ship-wakes excited by a swift electron perpendicularly impacting upon and moving parallel above a graphene monolayer, respectively. 2D plasmons have fueled substantial research efforts in the past few years. Recent studies have identified that 2D plasmons exhibit peculiar dispersion that is formally analogous to hydrodynamic deep-water-waves on a 2D liquid surface. Logically, many intricate and intriguing hydrodynamic wave phenomena, such as the splashing stimulated by a droplet or stone impacting a calm liquid surface and the V-shaped ship-wakes generated behind a ship when it travels over a water surface, should have counterparts in 2D plasmons, but have not been studied. We fill this gap by investigating dynamic excitation of graphene plasmons when a monolayer graphene is perpendicularly impacted by a swift electron, as an analogue of hydrodynamic splashing. A central jet-like rise, called "Rayleigh jet" or "Worthington jet" as a hallmark in hydrodynamic splashing, is demonstrated as an excessive concentration of graphene plasmons, followed by plasmonic ripples dispersing like concentric ripples of deep-water waves. This plasmonic jet, serving as a monopole antenna, can generate radiation as analogue of splashing sound. This is also the first discussion on the space-time limitation on surface plasmon generation. We then demonstrate a V-shaped plasmonic wave pattern when a swift electron moves parallel above a graphene monolayer, as an analogue of hydrodynamic ship-wakes. The plasmonic wake angle is found to be the same with the Kelvin angle and thus insensitive to the electron velocity when the electron velocity is small. However, the wake angle gradually decreases by increasing the electron's velocity when the electron velocity is large, and thus transits into the Mach angle, being similar to recent development in fluid

  13. Doppler Velocimetry of Current Driven Spin Helices in a Two-Dimensional Electron Gas

    Science.gov (United States)

    Yang, Luyi

    Spins in semiconductors provide a pathway towards the development of spin-based electronics. The appeal of spin logic devices lies in the fact that the spin current is even under time reversal symmetry, yielding non-dissipative coupling to the electric field. To exploit the energy-saving potential of spin current it is essential to be able to control it. While recent demonstrations of electrical-gate control in spin-transistor configurations show great promise, operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high mobility semiconductors used for devices. This thesis presents the demonstration and application of a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization at the level of 1 nm on a picosecond time scale. We discuss experiments in which this technique is used to measure the motion of spin helices in high mobility n-GaAs quantum wells as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. We find that the spin helix velocity changes sign as a function of wave vector and is zero at the wave vector that yields the largest spin lifetime. This observation is quite striking, but can be explained by the random walk model that we have developed. We discover that coherent spin precession within a propagating spin density wave is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. We report that, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the two-dimensional electron gas, spin diffusion is strongly suppressed

  14. Current instabilities under HF electron gas heating in semiconductors with negative differential conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, Yu. G.; Logvinov, G. N. [Instituto Politecnico Nacional, Mexico, D.F. (Mexico); Laricheva, N. [Datmouth College, New Hampshire (United States); Mashkevich, O. L. [Kharkov University, Kharkov (Ukraine)

    2001-10-01

    A nonlinear temperature dependence of the kinetic coefficients of semiconductor plasma can result in the appearance of regions of negative differential conductivity (NDC) in both the high-frequency (HF) and static current-voltage characteristics (CVC). In the present paper the formation of the static NDC under simultaneous electron gas heating by HF and static electric field is studied. As is shown below, in this case the heating electromagnetic wave has a pronounced effect on the appearance of NDC caused by the overheating mechanisms and the type of the static CVC as a whole. [Spanish] Una dependencia no lineal de la temperatura de los coeficientes cineticos del plasma del semiconductor puede llevar a la aparicion de regiones con conductividad diferencial negativa (CDN) en las caracteristicas corriente voltaje (CCV) de alta frecuencia (AF) y estatica. En este articulo se estudia la formacion de la CDN estatica bajo la accion simultanea del calentamiento del gas de electrones por AF y el campo electrico estatico. Como se muestra mas adelante, en este caso la onda electromagnetica que calienta a los electrones ejerce un fuerte efecto en la aparicion de la CDN; que se obtiene por mecanismos de sobrecalentamiento, y en el tipo de CCV estatica.

  15. Magnetic susceptibility and Landau diamagnetism of a quantum collisional Plasmas with arbitrary degree of degeneration of electronic gas

    CERN Document Server

    Latyshev, A V

    2013-01-01

    The kinetic description of magnetic susceptibility and Landau diamagnetism of quantum collisional plasmas with any degeration of electronic gas is given. The correct expression of electric conductivity of quantum collisional plasmas with any degeration of electronic gas (see A. V. Latyshev and A. A. Yushkanov, Transverse electrical conductivity of a quantum collisional plasma in the Mermin approach. - Theor. and Math. Phys., V. 175(1):559-569 (2013)) is used.

  16. Detection of irradiated fruits and vegetables by gas-chromatographic methods and electron spin-resonance

    Energy Technology Data Exchange (ETDEWEB)

    Farag, S.E.A. (National Centre for Radiation Research and Technology, Cairo (Egypt))

    1993-01-01

    Gas chromatographic methods detected some hydrocarbons esp. 17:1, 16:2, 15:0 and 14:1 in irradiated, Avocado, Papaya, Mangoes with 0.75, 1.5, 3.0 kGy and Apricot with 0.5 and 3.0 kGy. The detection of hydrocarbons was clearly at high doses but the low doses need more sensitive conditions using Liquid-Liquid-Gas chromatographic method as used here. Using Electron Spin-Resonance, produce a specific signal from irradiated onion (dried leaves) as well as apricot (hard coat of kernels) after some weeks of irradiation process but not clear with the other foodstuffs. (orig.)

  17. Construction of a Gas Electron Multiplier (GEM) Detector for Medical Imaging

    CERN Document Server

    Mondal, N N; Mazumdar, M R Dutta; Dubey, A K; Vioygi, Y P

    2013-01-01

    A prototype Gas Electron Multiplier (GEM) detector is under construction for medical imaging purposes. A single thick GEM of size 10x10 cm^2 is assembled inside a square shaped air-tight box which is made of Perspex glass. In order to ionize gas inside the drift field two types of voltage supplier circuits were fabricated, and array of 2x4 pads of each size 4x8 mm^2 were utilized for collecting avalanche charges. Preliminary testing results show that the circuit which produces high voltage and low current is better than that of low voltage and high current supplier circuit in terms of x-ray signal counting rates.

  18. Ultrafast electron diffraction from laser-aligned molecules in the gas phase

    Science.gov (United States)

    Yang, Jie

    Ultrafast electron diffraction has emerged since the end of last century, and has become an increasingly important tool for revealing great details of molecular dynamics. In comparison to spectroscopic techniques, ultrafast electron diffraction directly probes time-resolved structure of target molecules, and therefore can potentially provide "molecular movies" of the reactions being studied. These molecular movies are critical for understanding and ultimately controlling the energy conversion pathways and efficiencies of photochemical processes. In this dissertation, I have focused on ultrafast electron diffraction from gas-phase molecules, and have investigated several long-standing challenges that have been preventing researchers from being able to achieve 3-D molecular movies of photochemical reactions. The first challenge is to resolve the full 3-D structure for molecules in the gas phase. The random orientation of molecules in the gas phase smears out the diffraction signal, which results in only 1-D structural information being accessible. The second challenge lies in temporal resolution. In order to resolve coherent nuclear motions on their natural time scale, a temporal resolution of ˜200 femtosecond or better is required. However, due to experimental limitations the shortest temporal resolution that had been achieved was only a few picoseconds in early 2000, by Zewail group from Caltech. The first challenge is tackled by laser-alignment. In the first half of the dissertation, I approach this method both theoretically and experimentally, and demonstrate that by using a short laser pulse to transiently align target molecules in space, 3-D molecular structure can be reconstructed ab-initio from diffraction patterns. The second half of the dissertation presents two experiments, both of which are important steps toward imaging coherent nuclear motions in real time during photochemical reactions. The first experiment simultaneously resolves molecular alignment

  19. Infrared Line Emission from Molecular Gas Heated by X-Rays and Energetic Electrons

    Science.gov (United States)

    Maloney, Philip R.

    1997-01-01

    "I propose to carry out a detailed study using infrared observations (and in some cases, optical and ultraviolet observations) of dense interstellar gas exposed to intense fluxes of X-rays and/or energetic electrons. This is undoubtedly the dominant source of line emission for clouds exposed to X-rays from active galactic nuclei, supernova shocks, or embedded X-ray sources (e.g., X-ray binaries), or to high-temperature or relativistic electrons in galaxy clusters, near powerful radio sources, or supernova remnants. Detailed physical and chemical models of such clouds will be used to analyze infrared observations of the Great Annihilator X-ray source in the Galactic Center, cD galaxies in massive cooling flows, and the nuclei of Seyfert galaxies which will be obtained with the Infrared Space Observatory (ISO), UV and optical observations of the Crab Nebula obtained with the Hubble Space Telescope, and ground-based near-infrared observations of Seyfert nuclei. Results from this work will also be of great relevance to observations obtained with the Submillimeter Wave Astronomical Satellite (SWAS). In the first year of funding of this proposal, my chief collaborators (D.J. Hollenbach and A.G.G.M. Tielens, both of NASA Ames Research Center) and I concentrated on completing our models of the physical conditions in, and the resulting line emission from, dense gas irradiated by X-rays. As noted in the original proposal, some important physical processes were not yet thoroughly incorporated into our models at the time of submission. We completed our modeling of the physical conditions and line emission for essentially the entire range of parameter space (five orders of magnitude in X-ray flux to gas density ratio) occupied by typical dense interstellar clouds in which the gas is mostly neutral and X-rays are important for the ionization, chemistry, and thermal balance.

  20. Modified Monte Carlo method for study of electron transport in degenerate electron gas in the presence of electron-electron interactions, application to graphene

    Science.gov (United States)

    Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

    2017-07-01

    Standard computational methods used to take account of the Pauli Exclusion Principle into Monte Carlo (MC) simulations of electron transport in semiconductors may give unphysical results in low field regime, where obtained electron distribution function takes values exceeding unity. Modified algorithms were already proposed and allow to correctly account for electron scattering on phonons or impurities. Present paper extends this approach and proposes improved simulation scheme allowing including Pauli exclusion principle for electron-electron (e-e) scattering into MC simulations. Simulations with significantly reduced computational cost recreate correct values of the electron distribution function. Proposed algorithm is applied to study transport properties of degenerate electrons in graphene with e-e interactions. This required adapting the treatment of e-e scattering in the case of linear band dispersion relation. Hence, this part of the simulation algorithm is described in details.

  1. Piezoelectric Electromechanical Coupling in Nanomechanical Resonators with a Two-Dimensional Electron Gas

    Science.gov (United States)

    Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.

    2016-07-01

    The electrical response of a two-dimensional electron gas to vibrations of a nanomechanical cantilever containing it is studied. Vibrations of perpendicularly oriented cantilevers are experimentally shown to oppositely change the conductivity near their bases. This indicates the piezoelectric nature of electromechanical coupling. A physical model is developed, which quantitatively explains the experiment. It shows that the main origin of the conductivity change is a rapid change in the mechanical stress on the boundary between suspended and nonsuspended areas, rather than the stress itself.

  2. Electromechanical coupling in suspended nanomechanical resonators with a two-dimensional electron gas

    Science.gov (United States)

    Shevyrin, A. A.; Pogosov, A. G.; Bakarov, A. K.; Shklyaev, A. A.

    2017-06-01

    A physical model describing the piezoelectric-effect-mediated influence of bending of a thin suspended cantilever with a two-dimensional electron gas on the conductivity is proposed. The model shows that the conductivity change is almost entirely caused by the rapid change in mechanical stress near the boundary of suspended and non-suspended areas, rather than by the stress itself. An experiment confirming that the electromechanical coupling is associated with the piezoelectric effect is performed. The experimentally measured conductance sensitivity to the cantilever’s vibrations agree with the developed physical model.

  3. Ultra-low-temperature cooling of two-dimensional electron gas

    Science.gov (United States)

    Xia, J. S.; Adams, E. D.; Shvarts, V.; Pan, W.; Stormer, H. L.; Tsui, D. C.

    2000-05-01

    A new design has been used for cooling GaAs/Al xGa 1- xAs sample to ultra-low-temperatures. The sample, with electrical contacts directly soldered to the sintered silver powder heat exchangers, was immersed in liquid 3He, which was cooled by a PrNI 5 nuclear refrigerator. The data analysis shows that the two-dimensional electron gas (2DEG) was cooled to 4.0 mK at the refrigerator base temperature Tb of 2.0 mK. The design with heat exchanger cooling is applicable to any ultra-low-temperature transport measurements of 2DEG system.

  4. Spin injection into a two-dimensional electron gas using inter-digital-ferromagnetic contacts

    DEFF Research Database (Denmark)

    Hu, C.M.; Nitta, J.; Jensen, Ane;

    2002-01-01

    We present a model that describes the spin injection across a single interface with two electrodes. The spin-injection rate across a typical hybrid junction made of ferromagnet (FM) and a two-dimensional electron gas (2DEG) is found at the percentage level. We perforin spin-injection-detection ex......-injection-detection experiment on devices with two ferromagnetic contacts on a 2DEG confined in an InAs quantum well. A spin-injection rate of 4.5% is estimated from the measured magnetoresistance....

  5. Accurate exchange-correlation energies for the warm dense electron gas

    OpenAIRE

    Malone, FD; Blunt, NS; Brown, EW; Lee, DKK; Spencer, JS; Foulkes, WMC; Shepherd, JJ

    2016-01-01

    Density matrix quantum Monte Carlo (DMQMC) is used to sample exact-on-average $N$-body density matrices for uniform electron gas systems of up to 10$^{124}$ matrix elements via a stochastic solution of the Bloch equation. The results of these calculations resolve a current debate over the accuracy of the data used to parametrize finite-temperature density functionals. Exchange-correlation energies calculated using the real-space restricted path-integral formalism and the $k$-space configurati...

  6. Quantum spin-glass transition in the two-dimensional electron gas

    Indian Academy of Sciences (India)

    Subir Sachdev

    2002-02-01

    We discuss the possibility of spin-glass order in the vicinity of the unexpected metallic state of the two-dimensional electron gas in zero applied magnetic field. An average ferromagnetic moment may also be present, and the spin-glass order then resides in the plane orthogonal to the ferromagnetic moment. We argue that a quantum transition involving the destruction of the spin-glass order in an applied in-plane magnetic field offers a natural explanation of some features of recent magnetoconductance measurements. We present a quantum field theory for such a transition and compute its mean field properties.

  7. Electrically Detected Magnetic Resonance of Neutral Donors Interacting with a Two-Dimensional Electron Gas

    Energy Technology Data Exchange (ETDEWEB)

    Lo, C. C.; Lang, V.; George, R. E.; Morton, J. J. L.; Tyryshkin, A. M.; Lyon, A.; Bokor, J.; Schenkel, T.

    2011-04-20

    We have measured the electrically detected magnetic resonance of donor-doped silicon field-effect transistors in resonant X- (9.7 GHz) and W-band (94 GHz) microwave cavities. The two-dimensional electron gas (2DEG) resonance signal increases by two orders of magnitude from X- to W-band, while the donor resonance signals are enhanced by over one order of magnitude. Bolometric effects and spin-dependent scattering are inconsistent with the observations. We propose that polarization transfer from the donor to the 2DEG is the main mechanism giving rise to the spin resonance signals.

  8. Determination of fluoxetine and norfluoxetine in plasma by gas chromatography with electron-capture detection

    Energy Technology Data Exchange (ETDEWEB)

    Nash, J.F.; Bopp, R.J.; Carmichael, R.H.; Farid, K.Z.; Lemberger, L.

    1982-10-01

    This gas-chromatographic method for assay of fluoxetine and norfluoxetine in human plasma involves extraction of the drugs and use of a /sup 63/Ni electron-capture detector. The linear range of detection is 25 to 800 micrograms/L for each drug. Overall precision (CV) in the concentration range of 10 to 100 micrograms/L for both drugs was approximately 10%. Accuracy (relative error) in the same concentration range was approximately +10%. None of the commonly prescribed antidepressants or tranquilizers that we tested interfere with the assay.

  9. Zero-order crystallization in the Bethe-Fermi homework and electron gas problems

    Science.gov (United States)

    Cambiaggio, M. C.; De Llano, M.; Plastino, A.; Szybisz, L.; Ramírez, S.

    1980-04-01

    Single-determinantal states consisting of localized, non-overlapping single-particle orbitals are used in comparison with those made up of plane wave ones to show that neutron matter prefers a "crystalline" configuration beyond a density of around 0.07 fm -3 for the ν0 homework potential. The total energy is not too high above the best Jastrow-correlated calculations. No such effect is found for the ν1 homework potential. The analogous question for the electron gas is also studied.

  10. Hydrodynamic theory for quantum plasmonics: Linear-response dynamics of the inhomogeneous electron gas

    DEFF Research Database (Denmark)

    Yan, Wei

    2015-01-01

    We investigate the hydrodynamic theory of metals, offering systematic studies of the linear-response dynamics for an inhomogeneous electron gas. We include the quantum functional terms of the Thomas-Fermi kinetic energy, the von Weizsa¨cker kinetic energy, and the exchange-correlation Coulomb...... response of complex metallic nanostructures, including quantum effects, by adjusting theory parameters appropriately....... energies under the local density approximation. The advantages, limitations, and possible improvements of the hydrodynamic theory are transparently demonstrated. The roles of various parameters in the theory are identified. We anticipate that the hydrodynamic theory can be applied to investigate the linear...

  11. Thermodynamic magnetization of two-dimensional electron gas measured over wide range of densities

    OpenAIRE

    Reznikov, M.; Kuntsevich, A. Yu.; Teneh, N.; Pudalov, V. M.

    2011-01-01

    We report measurements of dm/dn in Si MOSFET, where m is the magnetization of the two-dimensional electron gas and n is its density. We extended the density range of measurements from well in the metallic to deep in the insulating region. The paper discusses in detail the conditions under which this extension is justified, as well as the corrections one should make to extract dm/dn properly. At low temperatures, dm/dn was found to be strongly nonlinear already in weak magnetic fields, on a sc...

  12. Resonant Peak Splitting for Ballistic Conductance in Two-Dimensional Electron Gas Under Electromagnetic Modulation

    Institute of Scientific and Technical Information of China (English)

    WANG Ru-Zhi; YAN Xiao-Hong

    2000-01-01

    By developing a transfer-matrix method, the resonant peaks splitting of ballistic conductance are investigated into the two-dimensional electron gas system with both electric and magnetic modulations of nanoscale periods. It is found that there exists the n-fold resonant peak splitting for ballistic conductance through n perpendicular magnetic barriers to n electric barriers. With a combination of m magnetic barriers and n electric barriers by increasing the amplitude of electric field, the folds of the splitting would shift from m - 1 to n - 1.

  13. Metrology for graphene and 2D materials

    Science.gov (United States)

    Pollard, Andrew J.

    2016-09-01

    The application of graphene, a one atom-thick honeycomb lattice of carbon atoms with superlative properties, such as electrical conductivity, thermal conductivity and strength, has already shown that it can be used to benefit metrology itself as a new quantum standard for resistance. However, there are many application areas where graphene and other 2D materials, such as molybdenum disulphide (MoS2) and hexagonal boron nitride (h-BN), may be disruptive, areas such as flexible electronics, nanocomposites, sensing and energy storage. Applying metrology to the area of graphene is now critical to enable the new, emerging global graphene commercial world and bridge the gap between academia and industry. Measurement capabilities and expertise in a wide range of scientific areas are required to address this challenge. The combined and complementary approach of varied characterisation methods for structural, chemical, electrical and other properties, will allow the real-world issues of commercialising graphene and other 2D materials to be addressed. Here, examples of metrology challenges that have been overcome through a multi-technique or new approach are discussed. Firstly, the structural characterisation of defects in both graphene and MoS2 via Raman spectroscopy is described, and how nanoscale mapping of vacancy defects in graphene is also possible using tip-enhanced Raman spectroscopy (TERS). Furthermore, the chemical characterisation and removal of polymer residue on chemical vapour deposition (CVD) grown graphene via secondary ion mass spectrometry (SIMS) is detailed, as well as the chemical characterisation of iron films used to grow large domain single-layer h-BN through CVD growth, revealing how contamination of the substrate itself plays a role in the resulting h-BN layer. In addition, the role of international standardisation in this area is described, outlining the current work ongoing in both the International Organization of Standardization (ISO) and the

  14. Electron gas quality at various (110)-GaAs interfaces as benchmark for cleaved edge overgrowth

    Science.gov (United States)

    Riedi, S.; Reichl, C.; Berl, M.; Alt, L.; Maier, A.; Wegscheider, W.

    2016-12-01

    We study molecular beam epitaxial growth on the unusual (110) surface of GaAs substrates as prerequisite for cleaved edge overgrown structures. We present the first systematic comparison of the quality of two dimensional electron systems on simultaneously overgrown (110) GaAs monitor wafers with ex situ as well as in situ cleaved (110) facets. Our study confirms that characterization of the monitor wafer is a valid benchmark for the magnetotransport characteristics of structures grown on cleaved facets. We show that deviating results can be traced back to (110) substrates of lower quality. We also demonstrate that the roughness of the in situ cleaved facets is decisive for the quality of the induced electron gas.

  15. The HERMES Polarized Hydrogen and Deuterium Gas Target in the HERA Electron Storage Ring

    CERN Document Server

    Airapetian, A; Akopov, Z; Amarian, M; Ammosov, V V; Andrus, A; Aschenauer, E C; Augustyniak, W; Avakian, R; Avetisian, A; Avetissian, E; Bailey, P; Baturin, V; Baumgarten, C; Beckmann, M; Belostotskii, S; Bernreuther, S; Bianchi, N; Blok, H P; Böttcher, Helmut B; Borisov, A; Bouwhuis, M; Brack, J; Brüll, A; Bryzgalov, V V; Capitani, G P; Chiang, H C; Ciullo, G; Contalbrigo, M; Dalpiaz, P F; De Leo, R; De Nardo, L; De Sanctis, E; Devitsin, E G; Di Nezza, P; Düren, M; Ehrenfried, M; Elalaoui-Moulay, A; Elbakian, G M; Ellinghaus, F; Elschenbroich, U; Ely, J; Fabbri, R; Fantoni, A; Feshchenko, A; Felawka, L; Fox, B; Franz, J; Frullani, S; Gärber, Y; Gapienko, G; Gapienko, V; Garibaldi, F; Garrow, K; Garutti, E; Gaskell, D; Gavrilov, G E; Karibian, V; Graw, G; Grebenyuk, O; Greeniaus, L G; Hafidi, K; Hartig, M; Hasch, D; Heesbeen, D; Henoch, M; Hertenberger, R; Hesselink, W H A; Hillenbrand, A; Hoek, M; Holler, Y; Hommez, B; Iarygin, G; Ivanilov, A; Izotov, A; Jackson, H E; Jgoun, A; Kaiser, R; Kinney, E; Kiselev, A; Königsmann, K C; Kopytin, M; Korotkov, V A; Kozlov, V; Krauss, B; Krivokhizhin, V G; Lagamba, L; Lapikas, L; Laziev, A; Lenisa, P; Liebing, P; Lindemann, T; Lipka, K; Lorenzon, W; Lü, J; Maiheu, B; Makins, N C R; Marianski, B; Marukyan, H O; Masoli, F; Mexner, V; Meyners, N; Miklukho, O; Miller, C A; Miyachi, Y; Muccifora, V; Nagaitsev, A; Nappi, E; Naryshkin, Yu; Nass, A; Negodaev, M A; Nowak, Wolf-Dieter; Oganessyan, K; Ohsuga, H; Orlandi, G; Pickert, N; Potashov, S Yu; Potterveld, D H; Raithel, M; Reggiani, D; Reimer, P E; Reischl, A; Reolon, A R; Riedl, C; Rith, K; Rosner, G; Rostomyan, A; Rubacek, L; Ryckbosch, D; Salomatin, Yu I; Sanjiev, I; Savin, I; Scarlett, C; Schäfer, A; Schill, C; Schnell, G; Schüler, K P; Schwind, A; Seele, J; Seidl, R; Seitz, B; Shanidze, R G; Shearer, C; Shibata, T A; Shutov, V B; Simani, M C; Sinram, K; Stancari, M D; Statera, M; Steffens, E; Steijger, J J M; Stewart, J; Stösslein, U; Tait, P; Tanaka, H; Taroian, S P; Tchuiko, B; Terkulov, A R; Tkabladze, A V; Trzcinski, A; Tytgat, M; Vandenbroucke, A; Van der Nat, P B; van der Steenhoven, G; Vetterli, Martin C; Vikhrov, V; Vincter, M G; Visser, J; Vogel, C; Vogt, M; Volmer, J; Weiskopf, C; Wendland, J; Wilbert, J; Ybeles-Smit, G V; Yen, S; Zihlmann, B; Zohrabyan, H G; Zupranski, P

    2004-01-01

    The HERMES hydrogen and deuterium nuclear-polarized gas targets have been in use since 1996 with the polarized electron beam of HERA at DESY to study the spin structure of the nucleon. Polarized atoms from a Stern-Gerlach Atomic Beam Source are injected into a storage cell internal to the HERA electron ring. Atoms diffusing from the center of the storage cell into a side tube are analyzed to determine the atomic fraction and the atomic polarizations. The atoms have a nuclear polarization, the axis of which is defined by an external magnetic holding field. The holding field was longitudinal during 1996-2000, and was changed to transverse in 2001. The design of the target is described, the method for analyzing the target polarization is outlined, and the performance of the target in the various running periods is presented.

  16. Cavity quantum electrodynamics with many-body states of a two-dimensional electron gas.

    Science.gov (United States)

    Smolka, Stephan; Wuester, Wolf; Haupt, Florian; Faelt, Stefan; Wegscheider, Werner; Imamoglu, Ataç

    2014-10-17

    Light-matter interaction has played a central role in understanding as well as engineering new states of matter. Reversible coupling of excitons and photons enabled groundbreaking results in condensation and superfluidity of nonequilibrium quasiparticles with a photonic component. We investigated such cavity-polaritons in the presence of a high-mobility two-dimensional electron gas, exhibiting strongly correlated phases. When the cavity was on resonance with the Fermi level, we observed previously unknown many-body physics associated with a dynamical hole-scattering potential. In finite magnetic fields, polaritons show distinct signatures of integer and fractional quantum Hall ground states. Our results lay the groundwork for probing nonequilibrium dynamics of quantum Hall states and exploiting the electron density dependence of polariton splitting so as to obtain ultrastrong optical nonlinearities.

  17. Terahertz Radiation Heterodyne Detector Using Two-Dimensional Electron Gas in a GaN Heterostructure

    Science.gov (United States)

    Karasik, Boris S.; Gill, John J.; Mehdi, Imran; Crawford, Timothy J.; Sergeev, Andrei V.; Mitin, Vladimir V.

    2012-01-01

    High-resolution submillimeter/terahertz spectroscopy is important for studying atmospheric and interstellar molecular gaseous species. It typically uses heterodyne receivers where an unknown (weak) signal is mixed with a strong signal from the local oscillator (LO) operating at a slightly different frequency. The non-linear mixer devices for this frequency range are unique and are not off-the-shelf commercial products. Three types of THz mixers are commonly used: Schottky diode, superconducting hot-electron bolometer (HEB), and superconductor-insulation-superconductor (SIS) junction. A HEB mixer based on the two-dimensional electron gas (2DEG) formed at the interface of two slightly dissimilar semiconductors was developed. This mixer can operate at temperatures between 100 and 300 K, and thus can be used with just passive radiative cooling available even on small spacecraft.

  18. 2D fluid simulations of interchange turbulence with ion dynamics

    DEFF Research Database (Denmark)

    Nielsen, Anders Henry; Madsen, Jens; Xu, G. S.

    2013-01-01

    In this paper we present a first principle global two-dimensional fluid model. The HESEL (Hot Edge SOL Electrostatic) model is a 2D numerical fluid code, based on interchange dynamics and includes besides electron also the ion pressure dynamic. In the limit of cold ions the model almost reduces...

  19. Behaviour of plasma with arbitrary degree of degeneration of electronic gas in a slab of conducting medium

    CERN Document Server

    Latyshev, A V

    2016-01-01

    The analytical solution of the boundary problem on behaviour (oscillations) of the electronic plasmas with arbitrary degree of degeneration of electronic gas in a slab of the conducting medium is received. The kinetic Vlasov---Boltzmann equation with integral of collisions type BGK (Bhatnagar, Gross and Krook) and Maxwell equation for electric field are applied. Mirror (reflections) boundary conditions are used.

  20. Test beam results of a low-pressure micro-strip gas chamber with a secondary-electron emitter

    Energy Technology Data Exchange (ETDEWEB)

    Kwan, S.; Anderson, D.F.; Zimmerman, J. [Fermi National Accelerator Lab., Batavia, IL (United States); Sbarra, C. [Istituto Nazionale di Fisica Nucleare, Pisa (Italy); Salomon, M. [TRIUMF, Vancouver, BC (Canada)

    1994-10-01

    We present recent results, from a beam test, on the angular dependence of the efficiency and the distribution of the signals on the anode strips of a low-pressure microstrip gas chamber with a thick CsI layer as a secondary-electron emitter. New results of CVD diamond films as secondary-electron emitters are discussed.

  1. Unified fluid model analysis and benchmark study for electron transport in gas and liquid analogs

    Science.gov (United States)

    Garland, N. A.; Cocks, D. G.; Boyle, G. J.; Dujko, S.; White, R. D.

    2017-07-01

    The interaction of plasmas with liquids requires an understanding of charged particle transport in both the gaseous and liquid phases. In this study we present a generalized fluid-equation framework to describe bulk electron transport in both gaseous and non-polar liquid environments under non-hydrodynamic non-equilibrium conditions. The framework includes liquid structural effects through appropriate inclusion of coherent scattering effects and adaption of swarm data to account for the modification to the scattering environment present in such systems. In the limit of low-densities it reduces to the traditional gas-phase fluid-equation model. Using a higher-order fluid model (four moments), it is shown that by applying steady state electron swarm data in both the gaseous and liquid phases, to close the system of equations and evaluate collisional rates, an improvement in macroscopic electron transport results over popular existing assumptions used. The failure of the local mean energy approximation in fluid models to accurately describe complex spatial oscillatory structures in both the gaseous and liquid phases is discussed in terms of the spatial variation of the electron distribution function itself.

  2. Calculation of Ground State Rotational Populations for Kinetic Gas Homonuclear Diatomic Molecules including Electron-Impact Excitation and Wall Collisions

    Energy Technology Data Exchange (ETDEWEB)

    David R. Farley

    2010-08-19

    A model has been developed to calculate the ground-state rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electron-impact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with non-equilibrating electron-impact effects. The resulting steady-state rotational distributions are generally Boltzmann for N≥3, with a rotational temperature between the wall and feed gas temperatures. The N=0,1,2 rotational level populations depend sensitively on the relative rates of electron-impact excitation versus wall collision and gas feed rates.

  3. Industrial Plant for Flue Gas Treatment with High Power Electron Accelerators

    Science.gov (United States)

    Chmielewski, Andrzej G.; Tyminski, Bogdan; Zimek, Zbigniew; Pawelec, Andrzej; Licki, Janusz

    2003-08-01

    Fossil fuel combustion leads to acidic pollutants, like SO2, NOx, HCl emission. Different control technologies are proposed however, the most popular method is combination of wet FGD (flue gas desulfurization) and SCR (selective catalytic reduction). First, using lime or limestone slurry leads to SO2 capture, and gypsum is a product. The second process where ammonia is used as reagent and nitrogen oxides are reduced over catalyst surface to gaseous nitrogen removes NOx. New advanced method using electron accelerators for simultaneous SO2 and NOx removal has been developed in Japan, the USA, Germany and Poland. Both pollutants are removed with high efficiency and byproduct can be applied as fertilizer. Two industrial plants have been already constructed. One in China and second in Poland, third one is under construction in Japan. Information on the Polish plant is presented in the paper. Plant has been constructed at Power Station Pomorzany, Szczecin (Dolna Odra Electropower Stations Group) and treats flue gases from two Benson boilers 60 MWe and 100 MWth each. Flow rate of the flue gas stream is equal to 270 000 Nm3/h. Four transformer accelerators, 700 keV electron energy and 260 kW beam power each were applied. With its 1.05 MW total beam power installed it is a biggest radiation facility over the world, nowadays. Description of the plant and results obtained has been presented in the paper.

  4. Gas adsorption, energetics and electronic properties of boron- and nitrogen-doped bilayer graphenes

    Science.gov (United States)

    Fujimoto, Yoshitaka; Saito, Susumu

    2016-10-01

    We study stabilities and electronic properties of several environmental polluting or toxic gas molecules (CO, CO2, NO, and NO2) adsorbed on B and N atoms in bilayer graphene using first-principles electronic-structure calculations. We find that NO and NO2 molecules can be bound chemically on B-doped bilayer graphene with large adsorption energies, while CO and CO2 molecules are not adsorbed chemically on B-doped one. In the case of the N-doped graphene, all four gases do not bind with chemical bonds but adsorb rather physically with small adsorption energies at long distances between gases and graphene. The adsorptions of NO and NO2 molecules on B-doped bilayer graphene induce the acceptor states above the Fermi energy, and we also find that the charge transfer takes place when the NO and the NO2 molecules are adsorbed. Thereby, the B-doped bilayer graphene is expected to be useful for NO and NO2 gas sensor materials.

  5. Electronic and Interfacial Properties of PD/6H-SiC Schottky Diode Gas Sensors

    Science.gov (United States)

    Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Bansal, Gaurav; Petit, Jeremy B.; Knight, Dak; Liu, Chung-Chiun; Wu, Qinghai

    1996-01-01

    Pd/SiC Schottky diodes detect hydrogen and hydrocarbons with high sensitivity. Variation of the diode temperature from 100 C to 200 C shows that the diode sensitivity to propylene is temperature dependent. Long-term heat treating at 425 C up to 140 hours is carried out to determine the effect of extended heat treating on the diode properties and gas sensitivity. The heat treating significantly affects the diode's capacitive characteristics, but the diode's current carrying characteristics are much more stable with a large response to hydrogen. Scanning Electron Microscopy and X-ray Spectrometry studies of the Pd surface after the heating show cluster formation and background regions with grain structure observed in both regions. The Pd and Si concentrations vary between grains. Auger Electron Spectroscopy depth profiles revealed that the heat treating promoted interdiffusion and reaction between the Pd and SiC dw broadened the interface region. This work shows that Pd/SiC Schottky diodes have significant potential as high temperature gas sensors, but stabilization of the structure is necessary to insure their repeatability in long-term, high temperature applications.

  6. Low-energy electron diffraction study of rare gas adsorption on metal surfaces

    Science.gov (United States)

    Caragiu, Mellita

    2000-10-01

    The method of Low Energy Electron Diffraction (LEED) is applied to the study of rare gas - metal systems. The emphasis is on the adsorption site of the adatoms on the substrate, as a result of controversial opinions on this matter arising both from theoretical approaches and previous experimental data. Contrary to the expectations, it is found that rare gases prefer low coordination sites when adsorbed in commensurate phases for practically all studied structures: Cu111 -3x3 R30°-Xe, Pt111- 3x3 R30°-Xe, Pd111 -3x3 R30° -Xe, Ag111 -7x 7R19.1° -4Ar, Cu110 - 41 02 -5Kran dCu110 - 61 02 -7Xe. Possible explanations for the rare gas behavior on metal substrates are reviewed. Besides the crucial information of the rare gas adsorption site, the LEED analysis provides structural (geometrical) parameters for the systems under study and several non-structural ones (e.g. vibrations of the atoms and inner potential of the crystal).

  7. Development of Fabric-Based Chemical Gas Sensors for Use as Wearable Electronic Noses

    Directory of Open Access Journals (Sweden)

    Thara Seesaard

    2015-01-01

    Full Text Available Novel gas sensors embroidered into fabric substrates based on polymers/ SWNT-COOH nanocomposites were proposed in this paper, aiming for their use as a wearable electronic nose (e-nose. The fabric-based chemical gas sensors were fabricated by two main processes: drop coating and embroidery. Four potential polymers (PVC, cumene-PSMA, PSE and PVP/functionalized-SWCNT sensing materials were deposited onto interdigitated electrodes previously prepared by embroidering conductive thread on a fabric substrate to make an optimal set of sensors. After preliminary trials of the obtained sensors, it was found that the sensors yielded a electrical resistance in the region of a few kilo-Ohms. The sensors were tested with various volatile compounds such as ammonium hydroxide, ethanol, pyridine, triethylamine, methanol and acetone, which are commonly found in the wastes released from the human body. These sensors were used to detect and discriminate between the body odors of different regions and exist in various forms such as the urine, armpit and exhaled breath odor. Based on a simple pattern recognition technique, we have shown that the proposed fabric-based chemical gas sensors can discriminate the human body odor from two persons.

  8. Electron attachment to DNA single strands: gas phase and aqueous solution

    Science.gov (United States)

    Gu, Jiande; Xie, Yaoming; Schaefer, Henry F.

    2007-01-01

    The 2′-deoxyguanosine-3′,5′-diphosphate, 2′-deoxyadenosine-3′,5′-diphosphate, 2′-deoxycytidine-3′,5′-diphosphate and 2′-deoxythymidine-3′,5′-diphosphate systems are the smallest units of a DNA single strand. Exploring these comprehensive subunits with reliable density functional methods enables one to approach reasonable predictions of the properties of DNA single strands. With these models, DNA single strands are found to have a strong tendency to capture low-energy electrons. The vertical attachment energies (VEAs) predicted for 3′,5′-dTDP (0.17 eV) and 3′,5′-dGDP (0.14 eV) indicate that both the thymine-rich and the guanine-rich DNA single strands have the ability to capture electrons. The adiabatic electron affinities (AEAs) of the nucleotides considered here range from 0.22 to 0.52 eV and follow the order 3′,5′-dTDP > 3′,5′-dCDP > 3′,5′-dGDP > 3′,5′-dADP. A substantial increase in the AEA is observed compared to that of the corresponding nucleic acid bases and the corresponding nucleosides. Furthermore, aqueous solution simulations dramatically increase the electron attracting properties of the DNA single strands. The present investigation illustrates that in the gas phase, the excess electron is situated both on the nucleobase and on the phosphate moiety for DNA single strands. However, the distribution of the extra negative charge is uneven. The attached electron favors the base moiety for the pyrimidine, while it prefers the 3′-phosphate subunit for the purine DNA single strands. In contrast, the attached electron is tightly bound to the base fragment for the cytidine, thymidine and adenosine nucleotides, while it almost exclusively resides in the vicinity of the 3′-phosphate group for the guanosine nucleotides due to the solvent effects. The comparatively low vertical detachment energies (VDEs) predicted for 3′,5′-dADP− (0.26 eV) and 3′,5′-dGDP− (0.32 eV) indicate that electron detachment

  9. Investigation of Vortex Structures in Gas-Discharge Nonneutral Electron Plasma: IV. Pulse Ejection of Electrons at the mutual interaction of Vortex Structures

    CERN Document Server

    Kervalishvili, N A

    2015-01-01

    The results of experimental investigations of the ejection of electrons from gas-discharge nonneutral electron plasma at interaction of vortex structures have been given. The periodical approach of vortex structures causes the ejection of electrons both from the vortex structures themselves and from the adjacent regions of electron sheath to the end cathodes of discharge device. The ejection takes place in the form of short and long pulses following each other. The nature of these pulses and the dynamics of interaction of vortex structures at their approach were studied.

  10. Spin splitting in 2D monochalcogenide semiconductors

    Science.gov (United States)

    Do, Dat T.; Mahanti, Subhendra D.; Lai, Chih Wei

    2015-11-01

    We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer ε-and γ -type, and odd-number β-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the Γ-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer β-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D’yakonov-Perel’ spin relaxation mechanism is also suppressed.

  11. Bedform characterization through 2D spectral analysis

    DEFF Research Database (Denmark)

    Lefebvre, Alice; Ernstsen, Verner Brandbyge; Winter, Christian

    2011-01-01

    characteristics using twodimensional (2D) spectral analysis is presented and tested on seabed elevation data from the Knudedyb tidal inlet in the Danish Wadden Sea, where large compound bedforms are found. The bathymetric data were divided into 20x20 m areas on which a 2D spectral analysis was applied. The most...... energetic peak of the 2D spectrum was found and its energy, frequency and direction were calculated. A power-law was fitted to the average of slices taken through the 2D spectrum; its slope and y-intercept were calculated. Using these results the test area was morphologically classified into 4 distinct...

  12. Doppler Velocimetry of Current Driven Spin Helices in a Two-Dimensional Electron Gas

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Luyi [Univ. of California, Berkeley, CA (United States)

    2013-05-17

    Spins in semiconductors provide a pathway towards the development of spin-based electronics. The appeal of spin logic devices lies in the fact that the spin current is even under time reversal symmetry, yielding non-dissipative coupling to the electric field. To exploit the energy-saving potential of spin current it is essential to be able to control it. While recent demonstrations of electrical-gate control in spin-transistor configurations show great promise, operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high mobility semiconductors used for devices. This dissertation presents the demonstration and application of a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization at the level of 1 nm on a picosecond time scale. We discuss experiments in which this technique is used to measure the motion of spin helices in high mobility n-GaAs quantum wells as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. We find that the spin helix velocity changes sign as a function of wave vector and is zero at the wave vector that yields the largest spin lifetime. This observation is quite striking, but can be explained by the random walk model that we have developed. We discover that coherent spin precession within a propagating spin density wave is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. We report that, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the two-dimensional electron gas, spin diffusion is strongly

  13. Effect of organic chain length on structure, electronic composition, lattice potential energy, and optical properties of 2D hybrid perovskites [(NH3)(CH2) n (NH3)]CuCl4, n = 2-9

    Science.gov (United States)

    Abdel-Aal, Seham K.; Kocher-Oberlehner, Gudrun; Ionov, Andrei; Mozhchil, R. N.

    2017-08-01

    Diammonium series of Cu hybrid perovskites of the formula [(NH3)(CH2) n (NH3)]CuCl4, n = 6-9 are prepared from an ethanolic solution in stoichiometric ratio 1:1 (organic/inorganic). Formation of the desired material was confirmed and characterizes by microchemical analysis, FTIR, XRD and XPS spectra. The structure consists of corner-shared octahedron [CuCl4]2- anion alternative by organic [(NH3)(CH2) n (NH3)]2+ cations. The organic and inorganic layers form infinite 2D sheet that are connected via NH···Cl hydrogen bond. The calculated lattice potential energy U pot (kJ/mol) and lattice enthalpy Δ H L (kJ/mol) are inversely proportional to the molecular volume V m (nm3) and organic chain length. Optical properties show strong absorption peak at UV-visible range. The band gap energy calculated using Kubelka-Munk equation shows the decrease of the energy gap as organic chain length increases. The introduction of bromide ion to [(NH3)(CH2) n (NH3)]CuCl2Br2 denoted 2C7CuCB hybrid has shifted the energy gap to lower values from 2.6 to 2.18 eV for 2C7CuCl (yellow) and 2C7CuCB (brown), respectively, at the same organic chain length. All elements of [(NH3)(CH2)9(NH3)]CuCl4 and [(NH3)(CH2)7(NH3)]CuCl2Br2 were found in XPS spectra, as well as valence band spectra.

  14. Effective NOx remediation from a surrogate flue gas using the US NRL Electra electron beam facility

    Science.gov (United States)

    Petrova, Tz. B.; Petrov, G. M.; Wolford, M. F.; Giuliani, J. L.; Ladouceur, H. D.; Hegeler, F.; Myers, M. C.; Sethian, J. D.

    2017-02-01

    Nitric oxide (NOx) emission is under restrictive federal regulations because of its negative impact on atmosphere, biosphere, and human health. Therefore, its removal has been a subject of extensive research to develop new efficient and cost effective techniques that can be applied on an industrial scale. In this work, we study both experimentally and theoretically an effective removal of NOx pollutants from a surrogate flue gas (SFG) using high power electron beam (e-beam) pulses. SFG is a simulant for exhaust from coal combustion power plants (82% N2, 6% O2, 12% CO2, and ˜100 ppm of NOx). The pulsed electron beam is generated using the United States Naval Research Laboratory Electra facility, which delivers e-beams with energies of ˜500 keV and a power pulse duration of ˜140 ns. During the e-beam irradiation, the energetic electrons generate a non-equilibrium plasma containing chemically active species, which then react with NOx to form harmless substances. A non-equilibrium time-dependent model is developed to describe NOx remediation from SFG. The model combines e-beam deposition rates obtained by solving the electron Boltzmann equation and extensive plasma chemistry modeling, which follows the species on a time scale from sub-nanoseconds to a few seconds. NOx decomposition as a function of electron beam parameters is studied. It is demonstrated experimentally that short (ns) pulses are the most efficient for NOx removal. A sharp reduction of NOx was measured with e-beam power deposition increasing, following the trend predicted by the model, achieving a 20 fold reduction to ˜5 ppm at energy deposition ˜20 J/l.

  15. Band Alignment of 2D Transition Metal Dichalcogenide Heterojunctions

    KAUST Repository

    Chiu, Ming Hui

    2016-09-20

    It is critically important to characterize the band alignment in semiconductor heterojunctions (HJs) because it controls the electronic and optical properties. However, the well-known Anderson\\'s model usually fails to predict the band alignment in bulk HJ systems due to the presence of charge transfer at the interfacial bonding. Atomically thin 2D transition metal dichalcogenide materials have attracted much attention recently since the ultrathin HJs and devices can be easily built and they are promising for future electronics. The vertical HJs based on 2D materials can be constructed via van der Waals stacking regardless of the lattice mismatch between two materials. Despite the defect-free characteristics of the junction interface, experimental evidence is still lacking on whether the simple Anderson rule can predict the band alignment of HJs. Here, the validity of Anderson\\'s model is verified for the 2D heterojunction systems and the success of Anderson\\'s model is attributed to the absence of dangling bonds (i.e., interface dipoles) at the van der Waal interface. The results from the work set a foundation allowing the use of powerful Anderson\\'s rule to determine the band alignments of 2D HJs, which is beneficial to future electronic, photonic, and optoelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Electrical transport of an AlGaN/GaN two-dimensional electron gas

    Energy Technology Data Exchange (ETDEWEB)

    Saxler, A.; Debray, P.; Perrin, R. [and others

    2000-07-01

    An Al{sub x}Ga{sub 1{minus}x}N/GaN two-dimensional electron gas structure with x = 0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. Hall effect measurements gave a sheet electron concentration of 5.1x10{sup 12} cm{sup {minus}2} and a mobility of 1.9 x 10{sup 4} cm{sup 2}/Vs at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.21 {+-} 0.006 m{sub 0} based on the temperature dependence of the amplitude of Shubnikov-de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3 x 10{sup {minus}12} s.

  17. Modifications in Structural, Electrical, Electronic and Mechanical Properties of Titanium Thin Films under different Gas Plasmas

    Science.gov (United States)

    Singh, Omveer; Dahiya, Raj P.; Malik, Hitendra K.

    2015-09-01

    In the recent past, Titanium thin films can be grown over different substrates such as silicon, glass and quartz by using versatile deposition techniques DC, RF sputtering, electronic beam and thermal evaporation etc. The grown films are then exposed in different gas environments for individual application. It has been found that Titanium nitride exhibits good chemical stability, mechanical and electrical properties. To investigate these properties in titanium nitride thin films, we have developed a new approach hot cathode arc discharge plasma system. By using this technique, we can measure plasma and nitriding parameters independently. In the present work, we have investigated gases mixture (Nitrogen, Argon and Hydrogen) effect on the structural, mechanical, electrical and electronic properties in plasma system. We have used 100% N2, 50% N2 + 50% Ar and 50% N2 + 50% H2 gases ratio for plasma nitriding. Structural and electronic structure properties are measured from X-ray diffractions (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. The surface morphology of these films were measured using Atomic Force Microscopy (AFM) and the nano-indentation mode is used to find out the hardness of the samples. Government of India.

  18. Band-structure engineering in conjugated 2D polymers.

    Science.gov (United States)

    Gutzler, Rico

    2016-10-26

    Conjugated polymers find widespread application in (opto)electronic devices, sensing, and as catalysts. Their common one-dimensional structure can be extended into the second dimension to create conjugated planar sheets of covalently linked molecules. Extending π-conjugation into the second dimension unlocks a new class of semiconductive polymers which as a consequence of their unique electronic properties can find usability in numerous applications. In this article the theoretical band structures of a set of conjugated 2D polymers are compared and information on the important characteristics band gap and valence/conduction band dispersion is extracted. The great variance in these characteristics within the investigated set suggests 2D polymers as exciting materials in which band-structure engineering can be used to tailor sheet-like organic materials with desired electronic properties.

  19. Space charge neutralization by electron-transparent suspended graphene.

    Science.gov (United States)

    Srisonphan, Siwapon; Kim, Myungji; Kim, Hong Koo

    2014-01-20

    Graphene possesses many fascinating properties originating from the manifold potential for interactions at electronic, atomic, or molecular levels. Here we report measurement of electron transparency and hole charge induction response of a suspended graphene anode on top of a void channel formed in a SiO2/Si substrate. A two-dimensional (2D) electron gas induced at the oxide interface emits into air and makes a ballistic transport toward the suspended graphene. A small fraction (>~0.1%) of impinging electrons are captured at the edge of 2D hole system in graphene, demonstrating good transparency to very low energy (graphene anode have the effect of neutralizing the electron space charge in the void channel. This charge compensation dramatically enhances 2D electron gas emission at cathode to the level far surpassing the Child-Langmuir's space-charge-limited emission.

  20. Enhanced gas sensing performance of electrospun Pt-functionalized NiO nanotubes with chemical and electronic sensitization.

    Science.gov (United States)

    Fu, Jiecai; Zhao, Changhui; Zhang, Junli; Peng, Yong; Xie, Erqing

    2013-08-14

    Pt-functionalized NiO composite nanotubes were synthesized by a simple electrospinning method, and their morphology, chemistry, and crystal structure have been characterized at the nanoscale. It was found that the Pt nanoparticles were dispersed uniformly in the NiO nanotubes, and the Pt-functionalized NiO composite nanotubes showed some dendritic structure in the body of nanotubes just like thorns growing in the nanotubes. Compared with the pristine NiO nanotube based gas sensor and other NiO-based gas sensors reported previously, the Pt-functionalized NiO composite nanotube based gas sensor showed substantially enhanced electrical responses to target gas (methane, hydrogen, acetone, and ethanol), especially ethanol. The NiO-Pt 0.7% composite nanotube based gas sensor displayed a response value of 20.85 at 100 ppm at ethanol and 200 °C, whereas the pristine NiO nanotube based gas sensor only showed a response of 2.06 under the same conditions. Moreover, the Pt-functionalized NiO composite nanotube based gas sensor demonstrated outstanding gas selectivity for ethanol against methane, hydrogen, and acetone. The reason for which the Pt-functionalized NiO composite nanotube based gas sensor obviously enhanced the gas sensing performance is attributed to the role of Pt on the chemical sensitization (catalytic oxidation) of target gases and the electronic sensitization (Fermi-level shifting) of NiO.

  1. Experimental study of electrical properties of ZnO nanowire random networks for gas sensing and electronic devices

    Science.gov (United States)

    Zhang, D.; Chava, S.; Berven, C.; Lee, S. K.; Devitt, R.; Katkanant, V.

    2010-07-01

    In this paper, we report on studying of ZnO nanowire mats as an electrical nanomaterial with particular interest in their interaction with various gas surroundings for gas sensing characteristics. The ZnO nanowires were synthesized on sapphire substrates using a horizontal tube furnace. The techniques of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS) were applied to determine the as-grown ZnO nanowires’ morphological and crystal structures, chemical composition and electronic states. Four-terminal current-voltage (I-V) measurements were used to examine the electrical conductance of the ZnO nanowire mats exposed to various testing gases with reference to the vacuum condition. Gas exposure experiments were conducted in a custom-built environmental chamber, which was filled with different testing gases. We observed the current being significantly influenced with ambient CO gas. The I-V behavior of CO gas was also found to be reversible and repeatable after the chamber evacuation, which indicates that the ZnO nanowire mats can be used for gas sensing purposes. A possible interactive model of nanowires and testing gas molecules is proposed to elucidate the sensing selective and sensitive mechanism for gas sensors.

  2. Experimental study of electrical properties of ZnO nanowire random networks for gas sensing and electronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, D.; Lee, S.K.; Devitt, R.; Katkanant, V. [California State University, Fresno, Department of Physics, Fresno, CA (United States); Chava, S.; Berven, C. [University of Idaho, Department of Physics, Moscow (United States)

    2010-07-15

    In this paper, we report on studying of ZnO nanowire mats as an electrical nanomaterial with particular interest in their interaction with various gas surroundings for gas sensing characteristics. The ZnO nanowires were synthesized on sapphire substrates using a horizontal tube furnace. The techniques of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS) were applied to determine the as-grown ZnO nanowires' morphological and crystal structures, chemical composition and electronic states. Four-terminal current-voltage (I-V) measurements were used to examine the electrical conductance of the ZnO nanowire mats exposed to various testing gases with reference to the vacuum condition. Gas exposure experiments were conducted in a custom-built environmental chamber, which was filled with different testing gases. We observed the current being significantly influenced with ambient CO gas. The I-V behavior of CO gas was also found to be reversible and repeatable after the chamber evacuation, which indicates that the ZnO nanowire mats can be used for gas sensing purposes. A possible interactive model of nanowires and testing gas molecules is proposed to elucidate the sensing selective and sensitive mechanism for gas sensors. (orig.)

  3. Hybrid Si/TMD 2D electronic double channels fabricated using solid CVD few-layer-MoS2 stacking for Vth matching and CMOS-compatible 3DFETs

    KAUST Repository

    Chen, Min Cheng

    2014-12-01

    Stackable 3DFETs such as FinFET using hybrid Si/MoS2 channels were developed using a fully CMOS-compatible process. Adding several molecular layers (3-16 layers) of the transition-metal dichalcogenide (TMD), MoS2 to Si fin and nanowire resulted in improved (+25%) Ion,n of the FinFET and nanowire FET (NWFET). The PFETs also operated effectively and the N/P device Vth are low and matched perfectly. The proposed heterogeneous Si/TMD 3DFETs can be useful in future electronics. © 2014 IEEE.

  4. Annotated Bibliography of EDGE2D Use

    Energy Technology Data Exchange (ETDEWEB)

    J.D. Strachan and G. Corrigan

    2005-06-24

    This annotated bibliography is intended to help EDGE2D users, and particularly new users, find existing published literature that has used EDGE2D. Our idea is that a person can find existing studies which may relate to his intended use, as well as gain ideas about other possible applications by scanning the attached tables.

  5. Port Adriano, 2D-Model Tests

    DEFF Research Database (Denmark)

    Burcharth, Hans F.; Andersen, Thomas Lykke; Jensen, Palle Meinert

    This report present the results of 2D physical model tests (length scale 1:50) carried out in a waveflume at Dept. of Civil Engineering, Aalborg University (AAU).......This report present the results of 2D physical model tests (length scale 1:50) carried out in a waveflume at Dept. of Civil Engineering, Aalborg University (AAU)....

  6. Structural Theory of 2-d Adinkras

    CERN Document Server

    Iga, Kevin

    2015-01-01

    Adinkras are combinatorial objects developed to study 1-dimensional supersymmetry representations. Recently, 2-d Adinkras have been developed to study 2-dimensional supersymmetry. In this paper, we classify all 2-d Adinkras, confirming a conjecture of T. H\\"ubsch. Along the way, we obtain other structural results, including a simple characterization of H\\"ubsch's even-split doubly even code.

  7. 2D-model of oxygen emissions lines for Europa

    Science.gov (United States)

    Cessateur, Gaël; Barthelemy, Mathieu; Lilensten, Jean; Rubin, Martin; Maggiolo, Romain; De Keyser, Johan

    2017-04-01

    The Jovian moon Europa is an interesting case study as an archetype for icy satellites, and will be one of the primary targets of the ESA JUICE mission which should be launched in 2022. Hosting a thin neutral gas atmosphere mainly composed of O2 and H2O, Europa can be studied by its airglow and dayglow emissions. A 1D photochemistry model has first been developed to assess the impact of the solar UV flux on the visible emission, such as the red and green oxygen lines (Cessateur et al. 2016). For limb polar viewing, red line emissions can reach a few hundreds of Rayleigh close to the surface. The impact of the precipitating electrons has also been studied. The density and temperature of the electrons are first derived from the multifluid MHD model from Rubin et al. (2015). A 2D emission model has thus been developed to estimate the airglow emissions. When electrons are the major source of the visible emissions, the solar UV flux can be responsible for up to 15% of those emissions for some specific line of sight. Oxygen emission lines in the UV have also been considered, such as 130.5 and 135.6 nm. For the latter, we did estimate some significant line emissions reaching 700 Rayleigh for a polar limb viewing angle close to the surface. Oxygen emission lines are significant (higher than 10 R) for altitudes lower than 100 km for all lines, except for the red line emissions where emissions are still above 10 R up to 200 km from the surface. A sensitivity study has also been performed in order to assess the impact of the uncertainties relative to the dissociative-excitation cross sections. Cessateur G, Barthelemy M & Peinke I. Photochemistry-emission coupled model for Europa and Ganymede. J. Space Weather Space Clim., 6, A17, 2016 Rubin, M., et al. Self-consistent multifluid MHD simulations of Europa's exospheric interaction with Jupiter's magnetosphere, J. Geophys. Res. Space Physics, 120, 3503-3524, 2015

  8. Spectroscopic ellipsometry thin film and first-principles calculations of electronic and linear optical properties of [(C9H19NH3)2PbI2Br2] 2D perovskite

    Science.gov (United States)

    Abid, H.; Hlil, E. K.; Abid, Y.

    2017-03-01

    In this study we report results of first-principles density functional calculations using the full-potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA) for the exchange-correlation energy to calculate electronic and linear optical properties of the (C9H19NH3)2PbI2Br2 compound. The linear optical properties, namely, the real ε1 (ω) and imaginary ε2 (ω) parts of dielectric function, the refractive index n (ω) and the extinction coefficient k (ω) are calculated and compared with experimental spectroscopic ellipsometry spectra. The reflectivity R (ω) and electron energy loss function L (ω) are calculated too. Our calculations performed for band structure and density of states show that the valence band maximum and conduction band minimum are located at Γ point resulting in a direct band gap of about (Γv -Γc) of 2.42 eV in good agreement with the experimental data. The investigated compound has a large uniaxial anisotropy of the dielectric function of about 0.0739 and a negative birefringence at zero energy Δn (0) =-0.11.

  9. Industrial applications of electron beam flue gas treatment—From laboratory to the practice

    Science.gov (United States)

    Chmielewski, Andrzej G.

    2007-08-01

    The electron beam technology for flue gas treatment (EBFGT) has been developed in Japan in the early 1980s. Later on, this process was investigated in pilot scale in the USA, Germany, Japan, Poland, Bulgaria and China. The new engineering and process solutions have been developed during the past two decades. Finally industrial plants have been constructed in Poland and China. The high efficiency of SO x and NO x removal was achieved (up to 95% for SO x and up to 70% for NO x) and by-product is a high quality fertilizer. Since the power of accelerators applied in industrial installation is over 1 MW and requested operational availability of the plant is equal to 8500 h in year, it is a new challenge for radiation processing applications.

  10. Electrochemical Testing of Gas Tungsten Arc Welded and Reduced Pressure Electron Beam Welded Alloy 22

    Energy Technology Data Exchange (ETDEWEB)

    Day, S D; Wong, F M G; Gordon, S R; Wong, L L; Rebak, R B

    2003-09-07

    Alloy 22 (N06022) is the material selected for the fabrication of the outer shell of the nuclear waste containers for the Yucca Mountain high-level nuclear waste repository site. A key technical issue in the Yucca Mountain waste package program has been the integrity of container weld joints. The currently selected welding process for fabricating and sealing the containers is the traditional gas tungsten arc welding (GTAW) or TIG method. An appealing faster alternative technique is reduced pressure electron beam (RPEB) welding. Standard electrochemical tests were carried on GTAW and RPEB welds as well as on base metal to determine their relative corrosion behavior in SCW at 90 C (alkaline), 1 M HCl at 60 C (acidic) and 1 M NaCl at 90 C (neutral) solutions. Results show that for all practical purposes, the three tested materials had the electrochemical behavior in the three tested solutions.

  11. Least Square Regression Method for Estimating Gas Concentration in an Electronic Nose System

    Directory of Open Access Journals (Sweden)

    Walaa Khalaf

    2009-03-01

    Full Text Available We describe an Electronic Nose (ENose system which is able to identify the type of analyte and to estimate its concentration. The system consists of seven sensors, five of them being gas sensors (supplied with different heater voltage values, the remainder being a temperature and a humidity sensor, respectively. To identify a new analyte sample and then to estimate its concentration, we use both some machine learning techniques and the least square regression principle. In fact, we apply two different training models; the first one is based on the Support Vector Machine (SVM approach and is aimed at teaching the system how to discriminate among different gases, while the second one uses the least squares regression approach to predict the concentration of each type of analyte.

  12. Ultrafast Spin Density Wave Transition in Chromium Governed by Thermalized Electron Gas

    Science.gov (United States)

    Nicholson, C. W.; Monney, C.; Carley, R.; Frietsch, B.; Bowlan, J.; Weinelt, M.; Wolf, M.

    2016-09-01

    The energy and momentum selectivity of time- and angle-resolved photoemission spectroscopy is exploited to address the ultrafast dynamics of the antiferromagnetic spin density wave (SDW) transition photoexcited in epitaxial thin films of chromium. We are able to quantitatively extract the evolution of the SDW order parameter Δ through the ultrafast phase transition and show that Δ is governed by the transient temperature of the thermalized electron gas, in a mean field description. The complete destruction of SDW order on a sub-100 fs time scale is observed, much faster than for conventional charge density wave materials. Our results reveal that equilibrium concepts for phase transitions such as the order parameter may be utilized even in the strongly nonadiabatic regime of ultrafast photoexcitation.

  13. Least square regression method for estimating gas concentration in an electronic nose system.

    Science.gov (United States)

    Khalaf, Walaa; Pace, Calogero; Gaudioso, Manlio

    2009-01-01

    We describe an Electronic Nose (ENose) system which is able to identify the type of analyte and to estimate its concentration. The system consists of seven sensors, five of them being gas sensors (supplied with different heater voltage values), the remainder being a temperature and a humidity sensor, respectively. To identify a new analyte sample and then to estimate its concentration, we use both some machine learning techniques and the least square regression principle. In fact, we apply two different training models; the first one is based on the Support Vector Machine (SVM) approach and is aimed at teaching the system how to discriminate among different gases, while the second one uses the least squares regression approach to predict the concentration of each type of analyte.

  14. Gas Classification Using Combined Features Based on a Discriminant Analysis for an Electronic Nose

    Directory of Open Access Journals (Sweden)

    Sang-Il Choi

    2016-01-01

    Full Text Available This paper proposes a gas classification method for an electronic nose (e-nose system, for which combined features that have been configured through discriminant analysis are used. First, each global feature is extracted from the entire measurement section of the data samples, while the same process is applied to the local features of the section that corresponds to the stabilization, exposure, and purge stages. The discriminative information amounts in the individual features are then measured based on the discriminant analysis, and the combined features are subsequently composed by selecting the features that have a large amount of discriminative information. Regarding a variety of volatile organic compound data, the results of the experiment show that, in a noisy environment, the proposed method exhibits classification performance that is relatively excellent compared to the other feature types.

  15. Electronic Wave Packet Interferometry of Gas Phase Samples: High Resolution Spectra and Collective Effects

    Science.gov (United States)

    Stienkemeier, Frank

    2017-06-01

    Time-resolved coherent spectroscopy has opened many new directions to study ultrafast dynamics in complex quantum systems. While most applications have been achieved in the condensed phase, we are focusing on dilute gas phase samples, in particular, on doped helium droplet beams. Isolation in such droplets at millikelvin temperatures provides unique opportunities to synthesize well-defined complexes, to prepare specific ro-vibronic states, and study their dynamics. To account for the small densities in our samples, we apply a phase modulation technique in order to reach enough sensitivity and a high spectral resolution in electronic wave packet interferometry experiments. The combination with mass-resolved ion detection enabled us e.g. to characterize vibrational structures of excimer molecules. By extending this technique we have observed collective resonances in samples of very low density (10^8 cm^{-3}). With a variant of this method, we are currently elaborating the implementation of nonlinear all-XUV spectroscopy.

  16. A high density two-dimensional electron gas in an oxide heterostructure on Si (001

    Directory of Open Access Journals (Sweden)

    E. N. Jin

    2014-11-01

    Full Text Available We present the growth and characterization of layered heterostructures comprised of LaTiO3 and SrTiO3 epitaxially grown on Si (001. Magnetotransport measurements show that the sheet carrier densities of the heterostructures scale with the number of LaTiO3/SrTiO3 interfaces, consistent with the presence of an interfacial 2-dimensional electron gas (2DEG at each interface. Sheet carrier densities of 8.9 × 1014 cm−2 per interface are observed. Integration of such high density oxide 2DEGs on silicon provides a bridge between the exceptional properties and functionalities of oxide 2DEGs and microelectronic technologies.

  17. On the role of the gas environment, electron-dose-rate, and sample on the image resolution in transmission electron microscopy

    DEFF Research Database (Denmark)

    Ek, Martin; Jespersen, Sebastian Pirel Fredsgaard; Damsgaard, Christian Danvad;

    2016-01-01

    The introduction of gaseous atmospheres in transmission electron microscopy offers the possibility of studying materials in situ under chemically relevant environments. The presence of a gas environment can degrade the resolution. Surprisingly, this phenomenon has been shown to depend on the elec...

  18. Formation of nitric oxide in an industrial burner measured by 2-D laser induced fluorescence

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, A.; Bombach, R.; Kaeppeli, B. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-06-01

    We have performed two-dimensional Laser Induced Fluorescence (2-D LIF) measurements of nitric oxide and hydroxyl radical distributions in an industrial burner at atmospheric pressure. The relative 2-D LIF data of NO were set to an absolute scale by calibration with probe sampling combined with gas analysis. (author) 3 figs., 7 refs.

  19. Simulation of ionization-front-forming process at injection of relativistic electron beam with a gas chamber

    Energy Technology Data Exchange (ETDEWEB)

    Dolya, S.N.; Zhidkov, E.P.; Rubin, S.B.; Semerdzhiev, Kh.I.

    1982-01-01

    The methodical work on creation of computer program for numerical study of the processes of forming and motion of a virtual cathode at the injection of relativistic electron beam into a short cylindrical chamber, filled with gas, has been carried out. The obtained plots of the distributions of fields, potential and density appearing out of ion and electron gas of the beam itself are presented. The dependence of cross-section ionization on the electron velocity has been taken into account at the calculation; the resonance contribution into summarized cross-section of ionization was simulated. It is shown that the injection into the chamber without gas, some oscillations of the virtual cathode are observed. At the presence of the final front of the beam, the fields level at the initial stage is smaller than for the beam with a sharp front. However, in some time the field amplitudes are compared. The motion of simulated probe ions in the chamber is analyzed.

  20. Twin characterisation using 2D and 3D EBSD

    Institute of Scientific and Technical Information of China (English)

    M. D. NAVE; J. J. L. MULDERS; A. GHOLINIA

    2005-01-01

    Electron backscatter diffraction (EBSD) is a superior technique for twin characterisation due to its ability to provide highly detailed classification (by generation, system and variant) of a significant number of twins in a relatively short time. 2D EBSD is now widely used for twin characterisation and provides quite good estimates of twin volume fractions under many conditions. Nevertheless, its accuracy is limited by assumptions that have to be made due to the 2D nature of the technique. With 3D EBSD, two key assumptions are no longer required, as additional information can be derived from the 3D map. This paper compares the benefits and limitations of 2D and 3D EBSD for twin characterisation. 2D EBSD enables a larger number of twins to be mapped in a given space of time, giving better statistics. 3D EBSD provides more comprehensive twin characterisation and will be a valuable tool for validation of 2D stereological methods and microstructural models of twinning during deformation.