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Sample records for tunnels electronic resource

  1. Tunneling electron trap

    International Nuclear Information System (INIS)

    The use of the field emission as means of filling the electron traps is proposed. Because of the electron tunneling at the cathode tip, the energy of the emitted electrons is lower than the electrostatic potential of the tip surface by the work function of the tip material. Consequently the electrons are trapped by the electrostatic well without requiring the dynamic trapping. The Brillouin density will be reached readily because the injection on the axis of the cylindrical symmetry dictates that the canonical angular momentum of the electrons vanishes. Furthermore the evaporative cooling due to the electrons escaping from the trap over the potential barrier may be able to cool the trapped electrons to cryogenic temperatures. The interesting regimes of the strongly correlated plasma and the quantum mechanical plasma may be obtained. (author)

  2. Long-range electron tunneling.

    Science.gov (United States)

    Winkler, Jay R; Gray, Harry B

    2014-02-26

    Electrons have so little mass that in less than a second they can tunnel through potential energy barriers that are several electron-volts high and several nanometers wide. Electron tunneling is a critical functional element in a broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic and respiratory charge transport chains. Prior to the 1970s, chemists generally believed that reactants had to collide in order to effect a transformation. Experimental demonstrations that electrons can transfer between reactants separated by several nanometers led to a revision of the chemical reaction paradigm. Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance. Theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers. Kinetics measurements have shown that electrons can tunnel about 2.5 nm through proteins on biologically relevant time scales. Longer-distance biological charge flow requires multiple electron tunneling steps through chains of redox cofactors. The range of phenomena that depends on long-range electron tunneling continues to expand, providing new challenges for both theory and experiment. PMID:24499470

  3. Resonant tunneling of electrons in quantum wires

    International Nuclear Information System (INIS)

    We considered resonant electron tunneling in various nanostructures including single wall carbon nanotubes, molecular transistors and quantum wires formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron-electron interaction in sequential and resonant electron tunneling are studied by using Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.

  4. Ponderomotive tunnelling in electron-laser interactions

    International Nuclear Information System (INIS)

    We have investigated the electron tunnelling of the ponderomotive potential by using the nonperturbative quantum electrodynamic and a modified Gaussian quantized field Volkov solution. We have shown that the electron can tunnel a ponderomotive potential, which is too wide to tunnel as a static barrier, by absorbing laser photons. The effect is quantized in nature: the tunnelled electron is discrete in both the energy spectra and diffraction patterns as a result of the multiphoton processes. A resonant tunnelling occurs when the ponderomotive energy equals the multiple integer of the laser photon energy. (fast track communication)

  5. Tunnel magnetoresistance and interfacial electronic state

    OpenAIRE

    Inoue, J.; Itoh, H.

    2002-01-01

    We study the relation between tunnel magnetoresistance (TMR) and interfacial electronic states modified by magnetic impurities introduced at the interface of the ferromagnetic tunnel junctions, by making use of the periodic Anderson model and the linear response theory. It is indicated that the TMR ratio is strongly reduced depending on the position of the $d$-levels of impurities, based on reduction in the spin-dependent $s$-electron tunneling in the majority spin state. Th...

  6. Interpretation of Electron Tunneling from Uncertainty Principle

    OpenAIRE

    Sarkar, Angik; Bhattacharyya, T. K.

    2005-01-01

    Beginners studying quantum mechanics are often baffled with electron tunneling.Hence an easy approach for comprehension of the topic is presented here on the basis of uncertainty principle.An estimate of the tunneling time is also derived from the same method.

  7. Resonant Tunneling with Electron-Phonon Interaction.

    Science.gov (United States)

    Wingreen, Ned Scott

    An exactly solvable model for resonant tunneling with electron-phonon interaction is presented and the results are compared with experimentally observed phonon-assisted resonant tunneling. While an electron tunnels through a localized state, it can exchange energy with the phonon system and thereby move closer to or farther from the resonance condition. As a result, the total transmission probability as a function of incident energy will depend on the electron -phonon interaction during tunneling. The transmission probability through a single resonant site coupled to phonons is solved for in the limit of a uniform density of states in the leads. To carry out the solution we employ S-matrix scattering theory and a Green function analysis of a localized state coupled to phonons. The presence of phonons alters the transmission spectrum by generating inelastic sidebands and suppressing the elastic tunneling resonance, but does not change the overall transmissivity of the tunneling structure. Contact is made with experiment by calculating the current transmitted through the resonant site including interaction with an Einstein band of optic phonons. The structure in the current-voltage characteristic for a coupling strength appropriate to GaAs reproduces the experimentally observed structure in the current for a GaAs/AlGaAs double -barrier heterostructure.

  8. Mobile Ventilation as a Tactic Resource at Tunnel Fires

    OpenAIRE

    Kumm, Mia; Bergqvist, Anders

    2008-01-01

    An emergency operation in case of a tunnel fire can easily become a complex operation. The objectives are to save people in danger, save the tunnel and its installations as well as vehicles trapped inside the tunnel and also, if it’s possible and necessary, reduce the effects on the environment. The strategy and the tactics in an emergency operation are very much depending on the specific tunnel, the fire behaviour and the resources from the fire brigade. One of the key factors is to ventilat...

  9. INELASTIC ENERGY LOSSES AT ELECTRON TUNNELING THROUGH POTENTIAL BARRIERS

    OpenAIRE

    Bakhtizin, R.; Valeyev, V.; Kukharenko, Yu

    1987-01-01

    An attempt was made to construct a simple theory of tunneling electron inelastic losses due to the excitation of electron-hole pairs, surface plasmons as well as to the excitation of electron transitions in adsorbed atoms and molecules.

  10. Theory of correlated electron transport and inelastic tunneling spectroscopy

    OpenAIRE

    Patton, Kelly R.

    2010-01-01

    For a non-superconducting system, the electronic tunneling current through an insulating barrier is calculated, including interaction effects. The exact Hamiltonian of the full system is projected onto the subspaces of the "left" and "right" leads. In the weak tunneling limit the well-known tunneling Hamiltonian is recovered, along with an additional term. This additional term originates from the projection of the electron-electron interaction onto each subsystem and corresp...

  11. Tunneling in the electron box in the nonperturbative regime

    International Nuclear Information System (INIS)

    We study charging effects and tunneling in the single electron box. Tunneling mixes different charge states and in the nonperturbative regime the charge in the island may be strongly screened. When charge states are nearly degenerate the screening of the charge is strong even in the weak tunneling regime. Virtual tunneling processes reduce both the level splitting ? and the tunneling strength ?. The charge on the island and the decay rates are calculated. In the strong tunneling regime also nondegenerate states are affected by tunneling. Strong-coupling scaling renormalizes the effective capacitance, a result which we confirm by Monte Carlo simulations. The tunneling strength ? scales to smaller values into the regime where the weak-coupling scaling applies. We propose a two-stage scaling procedure providing the unified picture for the problem. The scaling analysis is also extended to superconducting tunnel junctions with finite subgap conductance. ((orig.))

  12. Site-directed deep electronic tunneling through a molecular network

    International Nuclear Information System (INIS)

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors

  13. Electron tunneling in Bi2223 under high pressure

    International Nuclear Information System (INIS)

    We have studied the electron tunneling in Bi2223 break junctions under high pressure 0< P<10 kbar. A reproducible pressure influence on the linear conductance background has been found. We observed, that the normalized conductance vs voltage was increased with the pressure. This set of measurements seems to indicate that the linear tunneling conductance may have its explanation in the characteristics of the tunneling barrier namely on the resonant tunneling through the localized states in the insulating barrier

  14. Selection of Electronic Resources.

    Science.gov (United States)

    Weathers, Barbara

    1998-01-01

    Discusses the impact of electronic resources on collection development; selection of CD-ROMs, (platform, speed, video and sound, networking capability, installation and maintenance); selection of laser disks; and Internet evaluation (accuracy of content, authority, objectivity, currency, technical characteristics). Lists Web sites for evaluating…

  15. Wind resource accessment in complex terrain by wind tunnel modelling

    OpenAIRE

    Conan, Boris

    2012-01-01

    To benefit from strong winds, an increasing number of wind turbines are placed in complex terrains. But complex terrains means complex flows and difficult wind resource assessment. This study proposed to use wind tunnel modelling to evaluate the wind in a complex topography. The goal of this study is to evaluate the possibilities of wind resources assessment by wind tunnel modelling and to quantify the important modelling parameters. The lower part of the atmosphere, the atmospheric boundary ...

  16. Electron beam instabilities in gyrotron beam tunnels

    International Nuclear Information System (INIS)

    Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability, the Bernstein instability and the Langmuir instability. The low magnetic field gradient in drift tubes of QOG makes that the electron cyclotron maser instability can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the electrostatic Bernstein instability can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. (author) figs., tabs., refs

  17. Electron tunneling in carbon nanotube composites

    International Nuclear Information System (INIS)

    Nanocomposites, such as polymer blending with carbon nanotubes (CNTs), have been shown to have a drastic reduction in the resistivity and become conductive when the CNTs concentration has reached a certain percolation threshold. The reduction could be more than a millionth of the original polymer material. This has been realized as the formation of an infinite cluster of connected CNTs or pathways. Therefore, the conductivity of a nanocomposite should follow that of CNTs. Here we show that the resistivity of a nanocomposite is not governed by the interconnected CNTs, but the polymer between neighboring CNTs. That is, polymer-CNTs exhibit the nature of a conducting polymer, which can be explained as the tunneling of electrons one by one from the first CNT electrode to the next-nearest CNT electrode, forming a CNT/polymer pathway. A conduction model based on the tunneling of electrons passing, one by one, through the polymer gap between two neighboring CNT electrodes is formulated and derived. This model can accurately predict the significant reduction of the polymer-CNTs' resistivity with the addition of CNTs. The temperature effect can be readily incorporated to account for resistivity variation with the temperature of this nanocomposites.

  18. Spin polarized electron tunneling and magnetoresistance in molecular junctions.

    Science.gov (United States)

    Szulczewski, Greg

    2012-01-01

    This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered. PMID:21809185

  19. Human resources handbook [electronic resource].

    International Nuclear Information System (INIS)

    Contains documents related to human resources. Initial focus was on making available the rules (Charter, Staff Regulations, Staff Rules, Secretary-General's Bulletins, Administrative Instructions) pertaining to human resources. In addition, Information Circulars and links or references to already existing "Task Tools", such as forms and IMIS desk procedures, are included. Additional "Task Tools" are being placed online as they become available.

  20. Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach

    Science.gov (United States)

    Jacobs, Derya, A.; Aasen, Curtis A.

    2000-01-01

    Time, money, and, personnel are becoming increasingly scarce resources within government agencies due to a reduction in funding and the desire to demonstrate responsible economic efficiency. The ability of an organization to plan and schedule resources effectively can provide the necessary leverage to improve productivity, provide continuous support to all projects, and insure flexibility in a rapidly changing environment. Without adequate internal controls the organization is forced to rely on external support, waste precious resources, and risk an inefficient response to change. Management systems must be developed and applied that strive to maximize the utility of existing resources in order to achieve the goal of "faster, cheaper, better". An area of concern within NASA Langley Research Center was the scheduling, planning, and resource management of the Wind Tunnel Enterprise operations. Nine wind tunnels make up the Enterprise. Prior to this research, these wind tunnel groups did not employ a rigorous or standardized management planning system. In addition, each wind tunnel unit operated from a position of autonomy, with little coordination of clients, resources, or project control. For operating and planning purposes, each wind tunnel operating unit must balance inputs from a variety of sources. Although each unit is managed by individual Facility Operations groups, other stakeholders influence wind tunnel operations. These groups include, for example, the various researchers and clients who use the facility, the Facility System Engineering Division (FSED) tasked with wind tunnel repair and upgrade, the Langley Research Center (LaRC) Fabrication (FAB) group which fabricates repair parts and provides test model upkeep, the NASA and LARC Strategic Plans, and unscheduled use of the facilities by important clients. Expanding these influences horizontally through nine wind tunnel operations and vertically along the NASA management structure greatly increases the complexity of developing a model that can be used for successfully implementing a standardized management planning tool. The objective of this study was to implement an Integrated Wind Tunnel Planning System to improve the operations within the aeronautics testing and research group, in particular Wind Tunnel Enterprise. The study included following steps: Conducted literature search and expert discussions (NASA and Old Dominion University faculty), Performed environmental scan of NASA Langley wind tunnel operations as foundation for problem definition. Established operation requirements and evaluation methodologies. Examined windtunnel operations to map out the common characteristics, critical components, and system structure. Reviewed and evaluated various project scheduling and management systems for implementation, Evaluated and implemented "Theory of Constraints (TOC)" project scheduling methodology at NASA Langley wind tunnel operations together with NASA staff.

  1. Electron tunneling in chemistry chemical reactions over large distances

    CERN Document Server

    Khairutdinov, RF; Zhadanov, VP

    1989-01-01

    In Volume 30, an attempt is made to consider comprehensively both theoretical and experimental data that have been obtained to date on electron tunneling reactions involving chemical compounds of various classes, and to discuss the role played by these reactions in different areas of chemistry. The discussion of the above problem is preceded by a review of data on tunneling phenomena in nuclear physics, atomic physics, solid-state physics, as well as on the tunneling effects in chemistry that go beyond the framework of the main subject of this monograph. This review is included to acquaint the reader with the role of tunneling phenomena in physics and chemistry as a whole, to show how diversified the kingdom of tunneling phenomena is, and to see more distinctly the similarities and the differences between electron tunneling in chemical reactions and other tunnel phenomena.

  2. Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.

    Science.gov (United States)

    Nishino, Tomoaki

    2014-01-01

    This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

  3. Electron Tunneling Spectroscopy of Single and Bilayer Graphene with Hexagonal Boron Nitride Tunneling Barrier

    Science.gov (United States)

    Jung, Suyong; Park, Jaesung; Hwang, Chanyong; Ha, Donghan; Watanabe, Kenji; Taniguchi, Takashi; Moon, Pilkyung; Son, Young-Woo

    2015-03-01

    We have performed electron tunneling spectroscopy measurements on gated single and bilayer graphene devices with thin hexagonal boron nitride (h-BN) as a tunneling barrier. We can directly probe electronic structures of graphene devices by varying charge density and tunneling bias voltage. The evolution of bilayer energy gap identified as dI/dV dip in tunneling spectra is observed as the electric field between bottom gate and top tunneling probe varies. In addition, we can identify several spectra features which are in good agreement with the vibrational excitations; phonons of graphene and h-BN and a signature of local plasmonic excitation. Upon increasing external magnetic field, the development of Landau levels (LL) is observed as early as 0.2 T and we are able to discern individual LL as many as 20 as an index for both filled and empty states, which is unprecedented in previous tunneling spectroscopy studies on graphene devices.

  4. Many-body effects in magnetic inelastic electron tunneling spectroscopy

    OpenAIRE

    Korytár, Richard; Lorente, Nicolás; Gauyacq, Jean-Pierre

    2011-01-01

    Magnetic inelastic electron tunneling spectroscopy (IETS) shows sharp increases in conductance when a new conductance channel associated to a change in magnetic structure is open. Typically, the magnetic moment carried by an adsorbate can be changed by collision with a tunneling electron; in this process the spin of the electron can flip or not. A previous one-electron theory [Phys. Rev. Lett. {\\bf 103}, 176601 (2009)] successfully explained both the conductance thresholds a...

  5. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    Science.gov (United States)

    Hong, Woo-Pyo; Jung, Young-Dae

    2014-08-01

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

  6. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    International Nuclear Information System (INIS)

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed

  7. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

    2014-08-15

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

  8. Quantum tunneling and field electron emission theories

    CERN Document Server

    Liang, Shi-Dong

    2013-01-01

    Quantum tunneling is an essential issue in quantum physics. Especially, the rapid development of nanotechnology in recent years promises a lot of applications in condensed matter physics, surface science and nanodevices, which are growing interests in fundamental issues, computational techniques and potential applications of quantum tunneling. The book involves two relevant topics. One is quantum tunneling theory in condensed matter physics, including the basic concepts and methods, especially for recent developments in mesoscopic physics and computational formulation. The second part is the f

  9. Inelastic electron tunneling spectroscopy of local “spin accumulation” devices

    Energy Technology Data Exchange (ETDEWEB)

    Tinkey, Holly N.; Li, Pengke; Appelbaum, Ian, E-mail: appelbaum@physics.umd.edu [Department of Physics and CNAM, University of Maryland, College Park, Maryland 20742 (United States)

    2014-06-09

    We investigate the origin of purported “spin accumulation” signals observed in local “three-terminal” (3T) measurements of ferromagnet/insulator/n-Si tunnel junctions using inelastic electron tunneling spectroscopy (IETS). Voltage bias and magnetic field dependences of the IET spectra were found to account for the dominant contribution to 3T magnetoresistance, thus indicating that it arises from inelastic tunneling through impurities and defects at junction interfaces and within the barrier, rather than from spin accumulation due to pure elastic tunneling into bulk Si as has been previously assumed.

  10. Inelastic electron tunneling spectroscopy of local “spin accumulation” devices

    International Nuclear Information System (INIS)

    We investigate the origin of purported “spin accumulation” signals observed in local “three-terminal” (3T) measurements of ferromagnet/insulator/n-Si tunnel junctions using inelastic electron tunneling spectroscopy (IETS). Voltage bias and magnetic field dependences of the IET spectra were found to account for the dominant contribution to 3T magnetoresistance, thus indicating that it arises from inelastic tunneling through impurities and defects at junction interfaces and within the barrier, rather than from spin accumulation due to pure elastic tunneling into bulk Si as has been previously assumed.

  11. Klein tunneling in graphene: optics with massless electrons

    CERN Document Server

    Allain, P E

    2011-01-01

    This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-P\\'erot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. ...

  12. Electron-Photon interaction in resonant tunneling diodes

    OpenAIRE

    Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

    1997-01-01

    We develope a model to describe the transmission coefficient and tunneling current in the presence of photon-electron coupling in a resonant diode. Our model takes into account multiphoton processes as well as the transitions between electronic states with different wave numbers. This is crutial to explain the experimental features observed in the tunneling current through a double barrier which cannot be reproduced with more simplified established models. According to our r...

  13. Parity Effect and Tunnel Magnetoresistance of Ferromagnet / Superconductor / Ferromagnet Single-Electron Tunneling Transistors

    CERN Document Server

    Imamura, H; Ebisawa, H; Imamura, Hiroshi; Utsumi, Yasuhiro; Ebisawa, Hiromichi

    2002-01-01

    We theoretically study the tunnel magnetoresistance(TMR) of ferromagnet / superconductor / ferromagnet single-electron tunneling transistors with a special attention to the parity effect. It is shown that in the plateau region, there is no spin accumulation in the island even at finite bias voltage. However, the information of the injected spin is carried by the excess electron and thus the TMR exists. The spin relaxation rate of the excess electron can be estimated from the TMR. We also show that the TMR increases with decreasing the size of the superconducting island.

  14. Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces

    CERN Document Server

    Bullock, E T

    2000-01-01

    Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yi...

  15. Electronic processes in scanning tunneling microscopy of carbon nanotubes

    International Nuclear Information System (INIS)

    An LCAO theory of the tunneling current between carbon materials (sp2) and a metallic tip is developed to simulate their differential conductance and STM images. The tunneling current is expressed by a series expansion of the resolvent operator which is computed with a recursion algorithm. The differential conductance of both chiral and achiral nanotubes is calculated. We emphasize the fact that electronic and geometrical effects must be interpreted with much attention in STM imaging of carbon nanotubes

  16. Agripedia glossary [electronic resource].

    International Nuclear Information System (INIS)

    A glossary of terms used in the classes contained within Agripedia, an Internet accessible interactive multimedia instructional resource developed by the University of Kentucky's College of Agriculture.

  17. Spatiotemporal evolution of reaction fronts trigger by tunneling electrons

    International Nuclear Information System (INIS)

    Electron-induced reactions by means of STM techniques are performed. Pentaerytritol and explosives are deposited onto a Cu (110) surface. Chemical reactions are trigger by the tunneling electrons and can be detected via a phase modification of the molecular islands attached to the metal surface.

  18. Microwave-induced co-tunneling in single electron tunneling transistors

    DEFF Research Database (Denmark)

    Ejrnaes, M.; Savolainen, M.

    2002-01-01

    The influence of microwaves on the co-tunneling in single electron tunneling transistors has been investigated as function of frequency and power in the temperature range from 150 to 500 mK. All 20 low frequency connections and the RF line were filtered, and the whole cryostat was suspended on rubber bellows. Cross-talk was minimized by using individual coaxial lines between the sample and the room temperature electronics: The co-tunneling experiments were performed at zero DC bias current by measuring the voltage response to a very small amplitude 2 Hz current modulation with the gate voltage fixed at maximum Coulomb blockade. With the microwave signal applied to one side of the transistor, we find that the conductance increases linearly with T-2 and microwave power. (C) 2002 Elsevier Science B.V. All rights reserved.

  19. Electron-Photon interaction in resonant tunneling diodes

    CERN Document Server

    Iñarrea, J; Platero, G; Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

    1997-01-01

    We develope a model to describe the transmission coefficient and tunneling current in the presence of photon-electron coupling in a resonant diode. Our model takes into account multiphoton processes as well as the transitions between electronic states with different wave numbers. This is crutial to explain the experimental features observed in the tunneling current through a double barrier which cannot be reproduced with more simplified established models. According to our results, what experiments show in the current density are quantum photon-assisted features coming from multiphoton transitions which are not related with sample heating.

  20. Electron transport through thin film amorphous silicon: A tunneling study

    International Nuclear Information System (INIS)

    Electron tunneling through thin films of amorphous silicon (a-Si) is studied. Systematic studies were carried out of the conductance as a function of temperature, bias voltage and barrier thickness. It was found that the localized states in the amorphous silicon barrier, whose formation is due to the structural disorder, can have profound effects on the tunneling characteristics. At low temperatures and small bias (the ohmic regime), the localized states become resonant centers that enhance the tunneling probability greatly. This is marked by a crossover in the dominant tunneling mechanism, from direct tunneling to resonant tunneling as the barrier thickness increases. Increasing temperature or bias voltage enhances inelastic process due to, e.g., electron-phonon interaction. The favored conduction paths in this regime are isolated chains containing localized states that are nearly rectilinearly and equidistantly positioned across the tunnel barrier. Inelastic hopping through these chains gives rise to the voltage and temperature dependence of tunneling conductance which, to the lowest order, is predicted to be proportional to V4/3 and T4/3, respectively, corresponding to chains with two localized states. Convincing experimental evidence, both for the lowest order inelastic effects, and for crossover to higher order hopping channels with larger number of hops, is presented. Moreover, it was found that the threshold for the onset of inelastic effe threshold for the onset of inelastic effects is lowered for thicker barriers. As the barrier thickness and the temperature are further increased, the conductance acquires an asymptotic form which resembles the Mott Variable Range Hopping (VRH) behavior in the bulk limit. The crossover from inelastic hopping through isolated chains to the classical, random-walk-like VRH is discussed

  1. Fundamentals of Electronics Educational Resources

    Science.gov (United States)

    This website from UBM Tech provides links to a variety of technical papers, webinars, videos and tutorials pertaining to fundamental electronics. At the top of the page, users will find current spotlight resources.

  2. ELECTRONIC RESOURCES FOR THE HUMANITIES

    Directory of Open Access Journals (Sweden)

    Petrauskiene, Zibute

    2006-12-01

    Full Text Available Electronic information resources (EIR including electronic journals, books, and databases, as well as other different collections of information on the internet either paid or accessed for free withoutany doubt became one of the most important information resources in contemporary research and studies. The point is whether representatives of all fields of sciences use them with equal intensity and effectiveness. There is an opinion, that EIR are more applicable for physical, biomedical and technological sciences and representatives of these sciences are better prepared and use them much more extensively. It is thought that those, who study liberal arts, are technophobial, moreover, representatives of liberal arts themselves maintain that manuscript material is frequently moreimportant than electronic information, that books are primary and not articles.The aim of the article is to overview the peculiarity of representatives of liberal arts and to present an evaluated qualitative and acknowledged register of electronic information resources, which could be useful for representatives of liberal arts, ensure supplying of specific information needs and disseminate information about electronic information resources.To implement this goal the following tasks are solved in the article: problems of typology of electronic information resources are discussed and their original classification scheme presented based on theoretical and practical material; assessment criteria of electronic information resources are analyzed; an annotated list of electronic information resources for representatives of liberal arts is presented.The article may be relevant to the whole community of representatives of liberal arts: researchers, lecturers, students, as well as library specialists and others, interested in electronic information.

  3. Giant tunnel-electron injection in nitrogen-doped graphene

    DEFF Research Database (Denmark)

    Lagoute, Jerome; Joucken, Frederic

    2015-01-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling channel. At nitrogen sites, this feature vanishes due to an increase of the elastic channel that is allowed because of symmetry breaking induced by the nitrogen atoms. A large conductance enhancement by a factor of up to 500 was measured at the Fermi level by comparing local spectroscopy at nitrogen sites and at carbon sites. Nitrogen doping can therefore be proposed as a way to improve tunnel-electron injection in graphene.

  4. Microwave coupled electron tunneling measurement of Co nanoparticles

    OpenAIRE

    Jiang, W; Birk, F. Tijiwa; Davidovi?, D.

    2011-01-01

    We study electron tunneling through Co nanoparticles in the presence of repeated microwave pulses at 4.2K. While individual pulses are too weak to affect the magnetic switching field, repeated microwave pulses start to reduce the magnetic switching field at 10{\\mu}s spacing. We use I-V curve as a thermometer to show that the microwave pulses do not heat the sample, showing that magnetization in Co nanoparticles is directly excited by microwave pulses, and the relaxation time...

  5. Interplay between tunneling and exchange effects in the two electron double quantum dot molecule

    OpenAIRE

    Partoens, B; Matulis, A.; Peeters, F.M.

    1999-01-01

    The electronic structure of two vertically coupled quantum dots containing two electrons is investigated in the presence of interdot tunneling. Our approach also includes the interdot exchange and we find that the tunneling is affected by the Coulomb interaction. There is an interplay between direct tunneling, the interdot exchange and the Coulomb interaction influence on the tunneling, which can lead to a zero angular momentum spin-singlet - spin-triplet transition of the g...

  6. Room temperature observation of electron resonant tunneling through InAs/AlAs quantum dots

    OpenAIRE

    Sun, Jie; Li, Ruoyuan; ZHAO, CHANG; Yu, Like; Ye, Xiaoling; Xu, Bo; Chen, Yonghai; Wang, Zhanguo

    2007-01-01

    Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. Resonant tunneling current is superimposed on the thermal current, and they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77K or 300K, and this is the first time that resonant tunneling is observed at room t...

  7. Electron heating and quasiparticle tunneling in superconducting charge qubits

    International Nuclear Information System (INIS)

    We have directly measured non-equilibrium quasiparticle tunneling in the time domain as a function of temperature and RF carrier power for a pair of charge qubits based on the single Cooper-pair box, where the readout is performed with a multiplexed quantum capacitance technique. We have extracted an effective electron temperature for each applied RF power, using the data taken at the lowest power as a reference curve. This data has been fit to a standard T5 electron heating model, with a qualitative correspondence with established material parameters.

  8. Electron Heating and Quasiparticle Tunnelling in Superconducting Charge Qubits

    Science.gov (United States)

    Shaw, M. D.; Bueno, J.; Delsing, P.; Echternach, P. M.

    2008-01-01

    We have directly measured non-equilibrium quasiparticle tunnelling in the time domain as a function of temperature and RF carrier power for a pair of charge qubits based on the single Cooper-pair box, where the readout is performed with a multiplexed quantum capacitance technique. We have extracted an effective electron temperature for each applied RF power, using the data taken at the lowest power as a reference curve. This data has been fit to a standard T? electron heating model, with a reasonable correspondence with established material parameters.

  9. Scanning tunneling microscopy and inelastic electron tunneling spectroscopy studies of methyl isocyanide adsorbed on Pt(111)

    International Nuclear Information System (INIS)

    A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH3 stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

  10. Imaging Magnetic Tunnel Junctions Using Ballistic Electron Emission Microscopy

    Science.gov (United States)

    Perrella, A. C.; Rippard, W. H.; Buhrman, R. A.

    2001-03-01

    The high spatial resolution and sensitive energy dependence of ballistic electron emission microscopy (BEEM) make it a powerful tool for studying metal oxide metal tunnel junction systems. We have used this technique to study both evaporated and sputtered cobalt aluminum oxide cobalt thin films whose tunnel magnetoresistance and high impedance make these systems relevant to magnetic random access memory development. The excellent spatial resolution of BEEM allows us to image defects in these junctions, specifically we can determine the density and electrical properties of weak points, commonly referred to as ‘pinholes’, in these barriers as a function of aluminum thickness and oxidation conditions. The energy dependent transport through these barriers has been investigated through BEEM spectroscopy. This allows us to determine the effective barrier height of the aluminum oxide as well as the identity of specific defects. These defects are generally one of two types, either conducting columns that extend through the barrier or exposed cobalt that was oxidized during fabrication.

  11. Strong Coupling Between Single-Electron Tunneling and Nanomechanical Motion

    Science.gov (United States)

    Steele, G. A.; Hüttel, A. K.; Witkamp, B.; Poot, M.; Meerwaldt, H. B.; Kouwenhoven, L. P.; van der Zant, H. S. J.

    2009-08-01

    Nanoscale resonators that oscillate at high frequencies are useful in many measurement applications. We studied a high-quality mechanical resonator made from a suspended carbon nanotube driven into motion by applying a periodic radio frequency potential using a nearby antenna. Single-electron charge fluctuations created periodic modulations of the mechanical resonance frequency. A quality factor exceeding 105 allows the detection of a shift in resonance frequency caused by the addition of a single-electron charge on the nanotube. Additional evidence for the strong coupling of mechanical motion and electron tunneling is provided by an energy transfer to the electrons causing mechanical damping and unusual nonlinear behavior. We also discovered that a direct current through the nanotube spontaneously drives the mechanical resonator, exerting a force that is coherent with the high-frequency resonant mechanical motion.

  12. Electron tunneling in single layer graphene with an energy gap

    International Nuclear Information System (INIS)

    When a single layer graphene is epitaxially grown on silicon carbide, it will exhibit a finite energy gap like a conventional semiconductor, and its energy dispersion is no longer linear in momentum in the low energy regime. In this paper, we have investigated the tunneling characteristics through a two-dimensional barrier in a single layer graphene with an energy gap. It is found that when the electron is at a zero angle of incidence, the transmission probability as a function of incidence energy has a gap. Away from the gap the transmission coefficient oscillates with incidence energy which is analogous to that of a conventional semiconductor. The conductance under zero temperature has a gap. The properties of electron transmission may be useful for developing graphene-based nano-electronics. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  13. Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects

    International Nuclear Information System (INIS)

    In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C60 molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic strucend crucially on the lead electronic structure and junction geometry

  14. Tunneling through an Aharonov-Bohm ring -- effects of dephasing by electron-electron interactions

    CERN Document Server

    Zitko, R; Zitko, Rok; Bonca, Janez

    2002-01-01

    We develop a non-perturbative numerical method to study a single electron tunneling through an Aharonov-Bohm ring in the presence of bound, interacting electrons. Inelastic processes and spin-flip scattering are properly taken into account. We show that electron-electron interactions described by the Hubbard Hamiltonian lead to strong dephasing and we obtain high transmission probability at Phi=pi even at small interaction strength. Depending on the many-electron state on the ring, dephasing can occur in elastic or inelastic channels with or without changing the spin of the scattering electron.

  15. Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy

    OpenAIRE

    Becker, S.; Karrasch, C.; Mashoff, T.; Pratzer, M.; Liebmann, M.; Meden, V.; Morgenstern, M.

    2010-01-01

    Using low-temperature scanning tunneling spectroscopy applied to the Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe electron-electron interaction effects in the quantum Hall regime. The 2DES is decoupled from p-doped bulk states and exhibits spreading resistance within the insulating quantum Hall phases. In quantitative agreement with calculations we find an exchange enhancement of the spin splitting. Moreover, we observe that both the spatia...

  16. Crossover in tunneling hops in systems of strongly localized electrons

    International Nuclear Information System (INIS)

    Accurate Monte-Carlo simulation data show a consistent crossover in different characters of tunneling hops in two-dimensional systems of strongly localized electrons in the presence of scattering and quantum interference of hopping paths. The results also suggest a negative answer to the question whether there is a two-dimensional sign phase transition. The fractal behaviour observed in the direction perpendicular to the hopping direction is found to be similar to that for eigenstates in one-dimensional localized systems. (author). 16 refs, 6 figs

  17. Resonant Tunneling of Correlated Electrons in a Quantum Wire

    CERN Document Server

    Meden, V; Andergassen, S; Metzner, W; Schönhammer, K

    2005-01-01

    We study resonant tunneling of correlated electrons through a quantum wire containing a dot region. Within a fully microscopic model calculation the conductance G as a function of temperature T is determined over several decades. We identify parameter regimes in which the peak value G_p(T) shows distinctive power-law behavior. For intermediate dot parameters and T of the order of the level spacing of the dot we find that G_p(T) decreases (for decreasing T) in a non-universal way.

  18. Resonant tunneling of interacting electrons in an AC electric field

    International Nuclear Information System (INIS)

    The problem of the effect of electron-electron interaction on the static and dynamic properties of a double-barrier nanostructure (resonant tunneling diode (RTD)) is studied in terms of a coherent tunneling model, which includes a set of Schrödinger and Poisson equations with open boundary conditions. Explicit analytical expressions are derived for dc and ac potentials and reduced (active and reactive) currents in the quasi-classical approximation over a wide frequency range. These expressions are used to analyze the frequency characteristics of RTD. It is shown that the interaction can radically change the form of these expressions, especially in the case of a hysteretic I-V characteristic. In this case, the active current and the ac potentials can increase sharply at both low and high frequencies. For this increase to occur, it is necessary to meet quantum regime conditions and to choose a proper working point in the I-V characteristic of RTD. The possibility of appearance of specific plasma oscillations, which can improve the high-frequency characteristics of RTD, is predicted. It is found that the active current can be comparable with the resonant dc current of RTD

  19. Long-Distance Electron Tunneling in Proteins: A New Challenge for Time-Resolved Spectroscopy1

    OpenAIRE

    Stuchebrukhov, A. A.

    2010-01-01

    Long-distance electron tunneling is a fundamental process which is involved in energy generation in cells. The tunneling occurs between the metal centers in the respiratory enzymes, typically over distances up to 20 or 30 Å. For such distances, the tunneling time—i.e., the time during which an electron passes through the body of the protein molecule from one metal center to another—is of the order of 10 fs. Here the process of electron tunneling in proteins is reviewed, and a possibility of e...

  20. Collective Tunneling Model between Two-Dimensional Electron Gas to Si-Nano Dot

    Science.gov (United States)

    Muraguchi, M.; Sakurai, Y.; Takada, Y.; Nomura, S.; Shiraishi, K.; Makihara, K.; Ikeda, M.; Miyazaki, S.; Shigeta, Y.; Endoh, T.

    2011-12-01

    We study the temperature dependence of electron injection voltage in Si-Nano-Dot (Si-NDs) Floating Gate MOS capacitor by using the collective tunneling model, which models the tunneling between two-dimensional electron gas (2DEG) and the Si-NDs. We clarify the temperature dependence by numerical calculation, which emulate the experiment in this system, and we obtained a new insight into the origin of the temperature dependence. We have revealed that the collective tunneling model can reproduce the temperature dependence of electron tunneling.

  1. Phonon and plasmon excitation in inelastic electron tunneling spectroscopy of graphite

    OpenAIRE

    Vitali, Lucia; Schneider, M. A.; Kern, Klaus; Wirtz, Ludger; Rubio Secades, Ángel

    2003-01-01

    The inelastic electron tunneling spectrum (IETS)of highly oriented pyrolitic graphite (HOPG) has been measured with scanning tunneling spectroscopy (STS) at 6K. The observed spectral features are in very good agreement with the vibrational density of states (vDOS) of graphite calculated from first principles. We discuss the enhancement of certain phonon modes by phonon-assisted tunneling in STS based on the restrictions imposed by the electronic structure of graphite. We als...

  2. Determination of the tunnel rates through a few-electron quantum dot

    OpenAIRE

    Hanson, R; Vink, I. T.; DiVincenzo, D.P.; Vandersypen, L.M.K.; Elzerman, J. M.; van Beveren, L. H. Willems; Kouwenhoven, L.P.

    2004-01-01

    We demonstrate how rate equations can be employed to find analytical expressions for the sequential tunneling current through a quantum dot as a function of the tunnel rates, for an arbitrary number of states involved. We apply this method at the one-to-two electron transition where the electron states are known exactly. By comparing the obtained expressions to experimental data, the tunnel rates for six transitions are extracted. We find that these rates depend strongly on ...

  3. Excitation of local magnetic moments by tunneling electrons

    Science.gov (United States)

    Gauyacq, Jean-Pierre; Lorente, Nicolás; Novaes, Frederico Dutilh

    2012-05-01

    The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These structures were revealed by STM experiments in IBM Almaden in the early 2000s for atomic adsorbates on CuN surfaces. The experiments consisted in the study of the changes in conductance caused by inelastic tunneling of electrons (IETS, inelastic electron tunneling spectroscopy). Manganese and Iron adatoms were shown to have different magnetic anisotropies induced by the substrate. More experiments by other groups followed up, showing that magnetic excitations could be detected in a variety of systems: e.g. complex organic molecules showed that their magnetic anisotropy was dependent on the molecular environment, piles of magnetic molecules showed that they interact via intermolecular exchange interaction, spin waves were excited on ferromagnetic surfaces and in Mn chains, and magnetic impurities have been analyzed on semiconductors. These experiments brought up some intriguing questions: the efficiency of magnetic excitations was very high, the excitations could or could not involve spin flip of the exciting electron and singular-like behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis; perturbation theories, sudden-approximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, many-body approaches were also used to decipher the interplay between inelastic processes and the Kondo effect. Spin torque transfer has been shown to be effective in changing spin orientations of an adsorbate in theoretical works, and soon after it was shown experimentally. More recently, the previously mentioned strong coupling approach was extended to treat the excitation of spin waves in atomic chains and the ubiquitous role of electron-hole pair creation in de-exciting spins on surfaces has been analyzed. This review article expounds these works, presenting the theoretical approach by the authors while trying to thoroughly review parallel theoretical and experimental works.

  4. On the mechanical origin of single electron tunneling feedback effects in suspended carbon nanotubes

    OpenAIRE

    Schmid, D. R.; Stiller, P. L.; Strunk, C.; Hu?ttel, A. K.

    2014-01-01

    In single electron tunneling through clean, suspended carbon nanotube devices at low temperature, distinct switching phenomena have regularly been observed. These can be explained via strong interaction of single electron tunneling and mechanical motion of the nanotube. We present evidence that the switching phenomena are absent if the sample is kept in a viscous medium, additionally supporting this interpretation.

  5. Non-classical microwave radiation generated by electron transport in a tunnel junction

    Science.gov (United States)

    Qassemi, Farzad; Thibault, Karl; Bertrand Reulet, Bertrand; Blais, Alexandre

    2014-03-01

    Electrons coupled to a bath of photons in a tunnel junction form an interesting platform for many-body quantum phenomena. Recently, squeezing of radiated electromagnetic field due to electron shot noise has been observed [G. Gasse et al PRL 111, 136601 (2013)]. To investigate the relation between photonic and electronic correlation functions, we develop an input-output theory for electron-photon system in a tunnel junction. We show the effect of electronic transport on the equation of motion for the photon fields giving rise to nonclassical effects. In particular, we demonstrate that by modulating the bias voltage across the tunnel junction we can squeeze the radiated light.

  6. Thermally stimulated tunneling of electrons from deep traps: a new phenomenon

    International Nuclear Information System (INIS)

    A new phenomenon of electron tunneling is reported. During the phosphorescence decay of MgO:Li:Eu 10-3 at 480 K it was observed that the electrons from 550K trapping group tunnel into shallow traps. This tunneling is evident from the peak in the decay curve. It is observed that the location of the peak depends on the ambient temperature, dose of excitation and thermal/ excitation history of the sample. It is observed that the charge nature of the trapping groups also determines the possibility of electron tunneling. Thermal stimulation is required in the form of a higher ambient temperature. It is shown that this type of tunneling is different from those known at present, namely the tunneling due to infrared and electric or magnetic field stimulation. (author)

  7. Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

    Science.gov (United States)

    Hipps, K. W.; Scudiero, L.

    2005-01-01

    A quantum-mechanical probe is essential to study the quantum world, which is provided by electron tunneling. A spectroscopic mapping to image the electron-transport pathways on a sub-molecular scale is used.

  8. High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters

    Directory of Open Access Journals (Sweden)

    Hsiao Hsuan Cheng

    2012-10-01

    Full Text Available Well-defined experimental and simulating single peak to valley current density ratio (PVCDR resonant tunneling electronic circuit (RTEC element is proposed in this research. The variation of passive element value in RTEC structure is explored using simulation method, which obtains the optimum PVCDR values about 66. The simulating peak current density (PCD value is such high as 38 mA. Even though the experimental PCD value is less, but the PVCDR value is as high as 22.5, which value is favorably compared with semiconductor resonant tunneling devices (RTDs in single PVCDR RTEC element. The obvious triple negative differential resistance (NDR is also completed using composition of three suitable single RTEC elements. Also, experimental triple PVCDR RTEC element significantly exhibits three NDR curves with obvious three PVCDR values about 3.4, 3.8, and 6.0, respectively. Both peak voltage (PV value and valley voltage (VV values of experimental triple PVCDR RTEC element is less than 2.8 V, which value is profitable in development of commercial product. Power consumption of triple PVCDR RTEC element is as low as 75.5 ?W, which low power consumption will shrink the difficulty of element packaging in heat dissipation.

  9. Electronic transport through EuO spin filter tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Jutong, Nuttachai; Eckern, Ulrich [Institut fuer Physik, Universitaet Augsburg, 86135 Augsburg (Germany); Rungger, Ivan; Sanvito, Stefano [School of Physics and CRANN, Trinity College Dublin, Dublin (Ireland); Schwingenschloegl, Udo [KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia (Saudi Arabia)

    2012-07-01

    Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.

  10. Determination of the tunnel rates through a few-electron quantum dot

    CERN Document Server

    Hanson, R; Di Vincenzo, D P; Vandersypen, L M K; Elzerman, J M; Van Beveren, L H W; Kouwenhoven, L P

    2004-01-01

    We demonstrate how rate equations can be employed to find analytical expressions for the sequential tunneling current through a quantum dot as a function of the tunnel rates, for an arbitrary number of states involved. We apply this method at the one-to-two electron transition where the electron states are known exactly. By comparing the obtained expressions to experimental data, the tunnel rates for six transitions are extracted. We find that these rates depend strongly on the spin and orbital states involved in the tunnel process.

  11. Tunneling electron induced chemisorption of copper phthalocyanine molecules on the Cu(111) surface

    International Nuclear Information System (INIS)

    The adsorption of up to one monolayer (ML) of copper phthalocyanine (CuPc) molecules on a room temperature Cu(111) surface has been studied using scanning tunneling microscopy (STM). Below 1 ML the molecules are in a fluid state and are highly mobile on the surface. At 1 ML coverage the molecules coalesce into a highly ordered 2D crystal phase. At sub-ML coverages, chemisorption of individual CuPc molecules can be induced through exposure to tunneling electrons at a tunneling bias voltage exceeding a threshold value. This tunneling electron induced effect has been exploited to perform molecular STM lithography

  12. Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscopy imaging

    International Nuclear Information System (INIS)

    We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes

  13. Managing electronic resources a LITA guide

    CERN Document Server

    Weir, Ryan O

    2012-01-01

    Informative, useful, current, Managing Electronic Resources: A LITA Guide shows how to successfully manage time, resources, and relationships with vendors and staff to ensure personal, professional, and institutional success.

  14. Shifts and dips in inelastic-electron-tunneling spectra due to the tunnel-junction environment

    International Nuclear Information System (INIS)

    In general, the tunnel-junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have been typically less than the linewidth of the peaks, and peaks intensities have been comparable to infrared and Raman intensities. Here we report a different situation for tunnel junctions containing molecules adsorbed on metal particles. Specifically, we find that different-top-metal electrodes give different tunneling spectra for CO on alumina-supported iron and rhodium particles. Though metals with similar atomic radii give similar spectra, metals with dissimilar atomic radii can give qualitatively different spectra. We also find anomalies concerning intensities. Specifically, for methyl isocyanide adsorbed on alumina-supported rhodium particles, the strongest peak in the infrared spectrum, the --NequivalentC stretching mode, appears as a dip in the tunneling spectrum

  15. Direct evidence of electron tunneling in the ionization of sputtered atoms

    International Nuclear Information System (INIS)

    Direct evidence has been obtained for electron tunneling between sputtered Cs+ ions and the solid surfaces from which they originate. Strong neutralization of the Cs+ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully

  16. Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot

    OpenAIRE

    Kang, Kicheon; B. I. Min

    1997-01-01

    Employing the Anderson impurity model, we study tunneling properties through an ideal quantum dot near the conductance minima. Considering the Coulomb blockade and the quantum confinement on an equal footing, we have obtained current contributions from various types of tunneling processes; inelastic cotunneling, elastic cotunneling, and resonant tunneling of thermally activated electrons. We have found that the inelastic cotunneling is suppressed in the quantum confinement l...

  17. Atomic and electronic structure in collapsed carbon nanotubes evidenced by scanning tunneling microscopy

    OpenAIRE

    Giusca, Ce; Tison, Y.; Silva, Srp

    2007-01-01

    The electronic behavior of a radially collapsed armchair carbon nanotube encountered by scanning tunneling microscopy experiments is presented in a study that probes the electronic changes directly associated with the atomically resolved structural perturbations. The finite density of states obtained through scanning tunneling spectroscopy at the Fermi energy when the interspacing of the flattened faces does not allow for bond formation suggests that the electronic properties are slightly mod...

  18. Electron Tunneling Pathways and Role of Adenine in Repair of Cyclobutane Pyrimidine Dimer by DNA Photolyase

    OpenAIRE

    Liu, Zheyun; Guo, Xunmin; Tan, Chuang; Li, Jiang; Kao, Ya-ting; Wang, Lijuan; Sancar, Aziz; Zhong, Dongping

    2012-01-01

    Electron tunneling pathways in enzymes are critical to their catalytic efficiency. Through electron tunneling, photolyase, a photoenzyme, splits UV-induced cyclobutane pyrimidine dimer into two normal bases. Here, we report our systematic characterization and analyses of photo-initiated three electron transfer processes and cyclobutane ring splitting by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. We observed the complete dynamics of the reacta...

  19. Long-range intervalence electron tunneling through fully saturated systems

    International Nuclear Information System (INIS)

    The compounds (?-2,8-dithiadispirol[3.1.3.1]decane)-decaamminediruthenium(II,II) hexafluorophosphate, [(NH3)5RuS2C8H12Ru(NH3)5](PF6)4, and (?-2,10-dithiatrispiro[3.1.1.3.1.1]tridecane)-decaamminediruthenium(II,II) hexafluorophosphate, [(NH3)5RuS2C11H16Ru(NH3)5](PF6)4, were prepared, and upon oxidation, their intervalence properties were measured. The spiro binuclear with three rings had an IT band at 808 nm (epsilon 9 +/- 1 M-1 cm-1) and that with four rings had an IT band at 690 nm (epsilon 2.3 +/- 0.7 M-1 cm-1). This compares with a band at 910 nm (epsilon 43 +/- 2) measured earlier for the two-ring spiro binuclear. The through-bond distances between ruthenium centers range from 11.3 to 17.5 angstrom. The values of the electron tunneling matrix elements were calculated from Hopfield's theory and were found to be 1.7 X 10-2, 6.8 X 10-3, and 3.1 X 10-3 eV for the two-ring, three-ring, and four-ring binuclears, respectively. These correspond to rate constants of 8.0 X 10-7, 4.9 X 10-6, and 3.5 X 10-4 s-1, respectively, for the three bi>1, respectively, for the three binuclears. The results are discussed in terms of long-range tunneling and are compared to results obtained in solid matrices and biological systems

  20. Electronic Resource Management Systems in Practice

    Science.gov (United States)

    Grogg, Jill E.

    2008-01-01

    Electronic resource management (ERM) systems have inundated the library marketplace. Both integrated library systems (ILS) vendors and subscription agents are now offering products and service enhancements that claim to help libraries efficiently manage their electronic resources. Additionally, some homegrown and open-source solutions have emerged…

  1. Implementing CORAL: An Electronic Resource Management System

    Science.gov (United States)

    Whitfield, Sharon

    2011-01-01

    A 2010 electronic resource management survey conducted by Maria Collins of North Carolina State University and Jill E. Grogg of University of Alabama Libraries found that the top six electronic resources management priorities included workflow management, communications management, license management, statistics management, administrative…

  2. Digital Preservation of Electronic Resources

    Directory of Open Access Journals (Sweden)

    Ramesh C. Gaur,

    2012-07-01

    Full Text Available Due to huge advances in information communication technologies (ICTs, there has been an astronomicalgrowth of e-resources—e-journals, e-books, online databases and so on; libraries spend phenomenally onacquisition of these e- resources as these are very popularly used by the students and researchers.Unfortunately, this growth is accompanied by many threats. Digital content (of the e- resources is fragile andnot durable. Its accessibility and use by future generations depends on technology which very rapidly evolvesand changes. Hence, ensuring access of e-resources for future generation of users is a big challenge forlibraries. The present paper highlights various problems of digital content and elaborates how digital preservationis more demanding and challenging than preserving print copies of journals. It also gives a bird’s eye viewof various projects initiated for archiving digital content of scholarly journals.

  3. The use of tunnel diodes in impulsion electronics

    International Nuclear Information System (INIS)

    The purpose of the paper is to describe the performance limits which can be expected with basic pulse systems using tunnel diodes. The first part of the paper studies the response of a tunnel diode to a current step, and to a square-wave current. The second part, as an illustration, describes some actual systems and their performance. (author)

  4. Low-frequency noise in single electron tunneling transistor

    DEFF Research Database (Denmark)

    Tavkhelidze, A.N.; Mygind, Jesper

    1998-01-01

    The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz = 10 Hz, we find the same input charge noise, typically QN = 5 × 10–4 e/Hz1/2 at 10 Hz, with and without the HF shielding. At lower frequencies, the noise is due to charge trapping, and the voltage noise pattern superimposed on the V(Vg) curve (voltage across transistor versus gate voltage) strongly depends on the background charge configuration resulting from the cooling sequence and eventual radio frequency (rf) irradiation.The measured noise spectra which show both 1/f and 1/f1/2 dependencies and saturation for f <100 mHz can be fitted by two-level fluctuators with Debye–Lorentzian spectra and relaxation times of order seconds. In some cases, the positive and negative slopes of the V(Vg) curve have different overlaid noise patterns. For fixed bias on both slopes, we measure the same noise spectrum, and believe that the asymmetric noise is due to dynamic charge trapping near or inside one of the junctions induced when ramping the junction voltage. Dynamic trapping may limit the high frequency applications of the SET transistor. Also reported on are the effects of rf irradiation and the dependence of the SET transistor noise on bias voltage. ©1998 American Institute of Physics.

  5. Carbon nanotubes: Nonlinear high-Q resonators with strong coupling to single-electron tunneling

    OpenAIRE

    Meerwaldt, Harold B.; Steele, Gary A.; Zant, Herre S. J.

    2012-01-01

    Carbon nanotubes (CNTs) are nonlinear high-Q resonators with strong coupling to single-electron tunneling. We begin by describing several methods to detect the flexural motion of a CNT resonator. Next, we illustrate how single-electron tunneling in quantum dot CNT resonators leads to sharp dips in the mechanical resonance frequency and significant damping. We discuss four different contributions to the nonlinear oscillation of a CNT resonator: beam-like mechanical nonlineari...

  6. Bilayer Insulator Tunnel Barriers for Graphene-Based Vertical Hot-electron Transistors

    OpenAIRE

    Vaziri, Sam; Belete, Melkamu; Litta, Eugenio Dentoni; Smith, Anderson; Lupina, Grzegorz; Lemme, Max C.; Östling, Mikael

    2015-01-01

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as the electron emitter in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielect...

  7. Distant electron tunneling controlled by external fields in molecular nano structures

    International Nuclear Information System (INIS)

    The influence of stochastic, periodic, and magnetic fields on a long-range electron tunneling in donor - bridge - acceptor and electrode - molecular wire - electrode structures is studied theoretically. The description of a bridge-mediated electron tunneling between donor and acceptor groups is shown to be possible via the introduction of effective transfer rates. The principal distinction in the dependence of low-temperature elastic and inelastic tunnel currents mediated by a molecular wire with bridging paramagnetic ions on an applied magnetic field is considered. The appearance of the field-induced inversion and suppression effects is widely discussed

  8. Electron tunnelling through single azurin molecules can be on/off switched by voltage pulses

    Science.gov (United States)

    Baldacchini, Chiara; Kumar, Vivek; Bizzarri, Anna Rita; Cannistraro, Salvatore

    2015-05-01

    Redox metalloproteins are emerging as promising candidates for future bio-optoelectronic and nano-biomemory devices, and the control of their electron transfer properties through external signals is still a crucial task. Here, we show that a reversible on/off switching of the electron current tunnelling through a single protein can be achieved in azurin protein molecules adsorbed on gold surfaces, by applying appropriate voltage pulses through a scanning tunnelling microscope tip. The observed changes in the hybrid system tunnelling properties are discussed in terms of long-sustained charging of the protein milieu.

  9. Phonon and plasmon excitation in inelastic electron tunneling spectroscopy of graphite

    CERN Document Server

    Vitali, L; Kern, K; Wirtz, L; Rubio, A

    2003-01-01

    The inelastic electron tunneling spectrum (IETS)of highly oriented pyrolitic graphite (HOPG) has been measured with scanning tunneling spectroscopy (STS) at 6K. The observed spectral features are in very good agreement with the vibrational density of states (vDOS) of graphite calculated from first principles. We discuss the enhancement of certain phonon modes by phonon-assisted tunneling in STS based on the restrictions imposed by the electronic structure of graphite. We also demonstrate for the first time the local excitation of surface-plasmons in IETS which are detected at an energy of 40 meV.

  10. Managing Electronic Resources with Open Source Software

    OpenAIRE

    Roën Janyk; Sandra Wong

    2012-01-01

    The Simon Fraser University Library has been a leader in developing open source solutions for libraries for more than a decade.  This session will provide an overview of the complex world of library systems (Link Resolvers, Knowledgebases, Integrated Library Systems, Electronic Resource Management Systems, Discovery Services, Off-campus authentication systems) used by the modern academic library to efficiently manage electronic resources.  The session will present perspectives from ...

  11. Modulations of electronic tunneling rates through flexible molecular bridges by a dissipative superexchange mechanism

    International Nuclear Information System (INIS)

    Long-range coherent electron transfer between a donor and an acceptor is often assisted by intermediate molecular bridge, via the superexchange tunneling mechanism. The effect of electronic-nuclear coupling intensity on the tunneling rate and mechanism is analyzed using a generalized spin-boson model, in which the two level system, representing the donor and the acceptor is coupled to a dissipative nuclear bath only indirectly, via additional N bridge sites. A Langevin-Schroedinger equation, based on a mean field approximation, is applied in order to study the corresponding many-body dynamics, and the results are supported by numerically exact calculations for a single nuclear bridge mode. At zero temperature and when the electron tunneling is slower than the nuclear motion, the main effect of electronic-nuclear coupling is the dissipation of electronic energy at the bridge into nuclear vibrations. At small coupling intensities, the electronic tunneling rate increases due to this dissipative mechanism, but as the coupling intensity increases the tunneling into the acceptor is suppressed and efficient dissipation leads to electronic trapping (solvation) at the bridge. This analysis agrees with numerous experimental and theoretical studies, emphasizing the importance of the nuclear bridge conformation and the bridge flexibility in controlling the electron transfer rate in donor-bridge-acceptor systems

  12. TJ training journal [electronic resource].

    International Nuclear Information System (INIS)

    Training Journal is the UK's only dedicated publication for the Training and Learning & Development Industry. Aimed at everyone from the head of corporate learning & development through to the independent trainer, Training Journal provides the industry with a huge resource of information. Having been established for over 40 years, Training Journal has always been at the forefront of the industry, discussing the latest trends and research and helping to shape opinion and drive

  13. Monash University Library Electronic Resources Directory: Extending the Library Catalogue to Access Electronic Resources.

    Science.gov (United States)

    Smith, Lisa

    1997-01-01

    Describes the Electronic Resources Directory of Monash University (Melbourne, Australia), designed for locating electronic resources of the library. It both provides information about these resources as well as direct links to them where appropriate. Use of the World Wide Web for the directory has obvious advantages for a university where global…

  14. Electron tunneling into Bi thin films under pressure

    International Nuclear Information System (INIS)

    We have studied the pressure dependence of the tunneling resistance of tunnel junctions between 300-nm-thick Bi films and 20-nm-thick films of Al deposited at room temperature. Native Al oxide formed by oxygen glow discharge provided the tunnel barrier. The resistance was measured as a function of voltage from 0 to about 1 V. Measurements were made from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 to about 8 kbar. The resistance decreases with increasing pressure in a way easily described by simple tunneling theory. In the resistance curves we observe pressure dependence of structure, which has in the past been associated with the pressure dependence of the Bi band structure

  15. Electronic effects in scanning tunnelling microscopy of metal-filled multiwalled carbon nanotubes

    International Nuclear Information System (INIS)

    We have used ultrahigh-vacuum scanning tunnelling microscopy to investigate the effects of Fe filling on the electronic structure of multiwalled carbon nanotubes (MWNTs). When imaged using constant current feedback, Fe-filled MWNTs exhibit striking contrast corrugations that strongly correlate to expected positions (from transmission electron microscopy) of the Fe fillings along the nanotubes. Furthermore, the corrugation in contrast corresponds to significant variations in local electronic structure as determined by tunnelling spectroscopy. These results suggest that inner cores of Fe-filled carbon nanotubes can exhibit considerable influence on the electronics of the outer shells of even large MWNTs

  16. Estimation of potential radiation damage to electronics units in the CLIC tunnel

    CERN Document Server

    Patapenka, Andrei

    2014-01-01

    An electronic unit is required for each CLIC “Two Beam Module”. This study aims to estimate the potential damage due to the prompt radiation to the electronics units installed inside the CLIC Main Linac tunnel. Sets of Monte-Carlo simulations have been done to estimate damage to electronics installed at various locations inside the tunnel. Continuous and point beam losses have been considered for CLIC Main and Drive beams. Lead and iron in combination with a polyethylene layer were investigated as a possible shielding. The upper limits of the estimated quantities are presented for stand alone and shielded electronics.

  17. Observation of negative differential resistance and single-electron tunneling in electromigrated break junctions

    International Nuclear Information System (INIS)

    We observed a negative differential resistance (NDR) along with single-electron tunneling (SET) in the electron transport of electromigrated break junctions with metal-free tetraphenylporphyrin (H2BSTBPP) at a temperature of 11 K. The NDR strongly depended on the applied gate voltages, and appeared only in the electron tunneling region of the Coulomb diamond. We could explain the mechanism of this new type of electron transport by a model assuming a molecular Coulomb island and local density of states of the source and the drain electrodes

  18. Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique

    CERN Document Server

    Scherer, H; Hinze, P; Samwer, B W; Zorin, A B; Niemeyer, J C; Weimann, Th.

    1999-01-01

    We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr tunnel junctions and SET transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x 60 nm^2 using a scanning transmission electron microscope for the e-beam exposure on Si_3N_4 membrane substrate. We discuss the electrical performance of the transistor samples as well as their noise behavior.

  19. Radiation Damage to Electronics in the Beam Tunnel of the Next Linear Collider

    International Nuclear Information System (INIS)

    Radiation damage to electronics in the Linac tunnel of the Next Linear Collider due to ionizing and non-ionizing effects has been estimated with detailed FLUKA simulations. Results for total dose deposited in silicon and for displacement damage by neutrons, protons and charged pions are presented. It is shown that non-radiation-hard electronics could be severely damaged unless sufficiently shielded against radiation. A scenario is proposed in which the electronic components are located in niches in the beam tunnel wall which are shielded by layers of polyethylene

  20. Radiation damage to electronics in the beam tunnel of the next linear collider

    International Nuclear Information System (INIS)

    Radiation damage to electronics in the linac tunnel of the Next Linear Collider due to ionising and non-ionising effects has been estimated with detailed FLUKA simulations. Results for total dose deposited in silicon and for displacement damage by neutrons, protons and charged pions are presented. It is shown that non-radiation-hard electronics could be severely damaged unless sufficiently shielded against radiation. A scenario is proposed in which the electronic components are located in niches in the beam tunnel wall which are shielded by layers of polyethylene. (authors)

  1. Multi-electron dynamics in the tunnel ionization of correlated quantum systems

    CERN Document Server

    Hollstein, Maximilian

    2015-01-01

    The importance of multi-electron dynamics during the tunnel ionization of a correlated quantum system is investigated. By comparison of the solution of the time-dependent Schr\\"odinger equation (TDSE) with the time-dependent configuration interaction singles approach (TDCIS), we demonstrate the importance of a multi-electron description of the tunnel ionization process especially for weakly confined quantum systems. Within this context, we observe that adiabatic driving by an intense light field can even enhance the correlations between still trapped electrons.

  2. Effects of disorder on electron tunneling through helical edge states

    OpenAIRE

    Sternativo, Pietro; Dolcini, Fabrizio

    2014-01-01

    A tunnel junction between helical edge states, realized via a constriction in a Quantum Spin Hall system, can be exploited to steer both charge and spin current into various terminals. We investigate the effects of disorder on the transmission coefficient $T_p$ of the junction, by modelling disorder with a randomly varying (complex) tunneling amplitude $\\Gamma_p=|\\Gamma_p| \\exp[i \\phi_p]$. We show that, while for a clean junction $T_p$ is only determined by the absolute valu...

  3. Sensitivity of Tunneling-Rotational Transitions in Ethylene Glycol to Variation of Electron-to-Proton Mass Ratio

    OpenAIRE

    Viatkina, A. V.; Kozlov, M. G.

    2014-01-01

    Ethylene glycol in its ground conformation has tunneling transition with the frequency about 7 GHz. This leads to a rather complicated tunneling-rotational spectrum. Because tunneling and rotational energies have different dependence on the electron-to-proton mass ratio $\\mu$, this spectrum is highly sensitive to the possible $\\mu$ variation. We used simple 14 parameter effective Hamiltonian to calculate dimensionless sensitivity coefficients $Q_\\mu$ of the tunneling-rotatio...

  4. Reduction of charge trapping and electron tunneling in SIMOX by supplemental implantation of oxygen

    International Nuclear Information System (INIS)

    Silicon-on-insulator, SOI, technologies are being aggressively pursued to produce high density, high speed, radiation tolerant electronics. The dielectric isolation of the buried oxide makes it possible to design integrated circuits that greatly minimize single event upset and eliminate dose-rate induced latchup and upset. The reduction of excess-silicon related defects in SIMOX by the supplemental implantation of oxygen has been examined. The supplemental implant is 6% of the oxygen dose used to form the buried oxide, and is followed by a 1,000 C anneal, in contrast to the >1,300 C anneal used to form the buried oxide layer of SIMOX. The defects examined include shallow electron traps, deep hole traps, and silicon clusters. The radiation-induced shallow electron and deep hole trapping are measured by cryogenic detrapping and isothermal annealing techniques. The low-field (3 to 6 MV/cm) electron tunneling is interpreted as due to a two phase mixture of stoichiometric SiO2 and Si clusters a few nm in size. Single and triple SIMOS samples have been examined. All of the defects are reduced by the supplemental oxygen processing. Shallow electron trapping is reduced by an order of magnitude. Because of the larger capture cross section for hole trapping, hole trapping is not reduced as much. The low-field electron tunneling due to Si clusters is also significantly reduced. Both uniform and nonuniform electron tunneling have been observed in SIMOX samples without ve been observed in SIMOX samples without supplement processing. In samples exhibiting only uniform tunneling, electron capture at holes has been observed. The nonuniform tunneling is superimposed upon the uniform tunneling and is characterized by current spiking

  5. Electron tunnelling phenomena in YPO4?:?Ce,Ln (Ln = Er, Ho, Nd, Dy)

    International Nuclear Information System (INIS)

    Electron tunnelling from an Ln2+-electron trap (Ln = Er, Nd, Ho, Dy) to a Ce4+-recombination centre is investigated experimentally and theoretically in YPO4?:?Ce3+,Ln3+. Low temperature thermoluminescence, fading and isothermal decay measurements for samples with concentrations of Ce and Ln ranging from 0.05 to 5.0% are analysed. We observe a temperature activated tunnelling that depends on type of Ln and concentration. Results are simulated with simple quantum mechanical concepts. The average distance between traps and centres is altered by the Ce and Ln concentrations. The higher the concentration, the higher the electron tunnelling probability which can be attributed to a shorter average Ce4+–Ln2+ distance. As a result, changes in the thermoluminescence characteristics like the fading rates and the isothermal decay curves are observed. (paper)

  6. Anisotropic magnetic field dependence of many-body enhanced electron tunnelling through a quantum dot

    CERN Document Server

    Vdovin, E E; Makarovsky, O; Patanè, A; Eaves, L; Henini, M; Mellor, C J; Benedict, K A; Airey, R; Khanin, Yu.N.

    2007-01-01

    We investigate the effect of an applied magnetic field on resonant tunneling of electrons through the bound states of self-assembled InAs quantum dots (QDs) embedded within an (AlGa)As tunnel barrier. At low temperatures (no more than 2 K), a magnetic field B applied either parallel or perpendicular to the direction of current flow causes a significant enhancement of the tunnel current. For the latter field configuration, we observe a strong angular anisotropy of the enhanced current when B is rotated in the plane of the quantum dot layer. We attribute this behavior to the effect of the lowered symmetry of the QD eigenfunctions on the electron-electron interaction.

  7. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    2010-01-01

    This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and width. This is related to the d-band model for catalytic reactions. The largest change is in the amplitude of the state, however the "reversed" structure of cobalt on Ag(111) show similar properties, but with a large shift in energy instead of amplitude. The Kondo eect is used to probe magnetic interaction between the aforementioned silver-capped cobalt islands (and additionally gold-capped cobalt islands) and single cobalt atoms positioned on the Moire pattern. A split Kondo resonance due to the exchange interaction between the island and the atom is observed. In a more technical section of the thesis, it is shown how a gold-coated STM tip will make the tip apex susceptible to a single cobalt atom. The tip is indented either directly in a Au(111) surface or gold akes are picked up from cobalt islands on Cu(111). A change in the local barrier height (work function) of the tip-sample junction indicates that the apex is gold-coated and a single cobalt atom can be pickup up. The cobalt atom attached to the tip displays a Kondo resonance formed between the atom and the tip similar to the resonance displayed when the atom is on the surface with a clean tip. Here, this is used to show how a two-impurity Kondo system consisting of two cobalt atoms, one on the tip and one on the Au(111) sample, is undergoing a continuous crossover from Kondo screened atoms to antiferromagnetically coupled atoms when the atoms are moved from non-interacting to strongly interacting. In the Kondo screened regime, the Kondo temperature is believed to be constant, but the Fano line ii shape changes continuously from a dip to a peak. In the antiferromagnetic regime, inelastic spin-ip excitations reveal a splitting with a continuous increase in energy levels when pushing the atoms further together. This is supported by numerical renormalization group calculations. The crossover between the two regimes is furthermore interesting because it occurs in an area of the phase diagram close to the elusive quantum critical point, where the phase transition line meets absolute zero temperature. This freely positionable Kondo system on the tip represents a novel way to probe magnetic interaction with the possibility to continuously change the position of the probing Kondo system. The experiment is believed to be one of many applications possible and the method opens up for a new eld within STM. We expect that our work has direct impact in other research areas, such as for heavy fermion materials, a class of materials whose properties are governed by the competition between Kondo screening an

  8. HIGH RESOLUTION ELECTRON BEAM INJECTION IN SEMICONDUCTORS USING A SCANNING TUNNELING MICROSCOPE

    OpenAIRE

    Alvarado, S.; Renaud, Ph; Meier, H.

    1991-01-01

    The tip of a scanning tunneling microscope is used as a source of ultralow-energy electrons to excite luminescence in model AlGaAs/GaAs(001) heterostructures. This beam injection technique has the advantage of providing a nanometer-sized charge generation volume. We demonstrate the application of this technique to determine minority charge carrier transport parameters such as the thermalization length of hot electrons and the diffusion length of minority electrons.

  9. Darwin at the molecular scale: selection and variance in electron tunnelling proteins including cytochrome c oxidase

    OpenAIRE

    Moser, Christopher C.; Page, Christopher C.; Dutton, P. Leslie

    2006-01-01

    Biological electron transfer is designed to connect catalytic clusters by chains of redox cofactors. A review of the characterized natural redox proteins with a critical eye for molecular scale measurement of variation and selection related to physiological function shows no statistically significant differences in the protein medium lying between cofactors engaged in physiologically beneficial or detrimental electron transfer. Instead, control of electron tunnelling over long distances relie...

  10. Effects of disorder on electron tunneling through helical edge states

    Science.gov (United States)

    Sternativo, Pietro; Dolcini, Fabrizio

    2014-09-01

    A tunnel junction between helical edge states, realized via a constriction in a quantum spin Hall system, can be exploited to steer both charge and spin current into various terminals. We investigate the effects of disorder on the transmission coefficient Tp of the junction by modeling disorder with a randomly varying (complex) tunneling amplitude ?p=|?p|exp[i?p]. We show that, while for a clean junction Tp is only determined by the absolute value |?p| and is independent of the phase ?p, the situation can be quite different in the presence of disorder: phase fluctuations may dramatically affect the energy dependence of Tp of any single sample. Furthermore, analyzing three different models for phase disorder (including correlated ones), we show that not only the amount but also the way the phase ?p fluctuates determines the localization length ?loc and the sample-averaged transmission. Finally, we discuss the physical conditions in which these three models suitably apply to realistic cases.

  11. Real-time detection of single electron tunneling using a quantum point contact

    CERN Document Server

    Vandersypen, L M K; Schouten, R N; Willems van Beveren, L H; Hanson, R; Kouwenhoven, L P

    2004-01-01

    We observe individual tunnel events of a single electron between a quantum dot and a reservoir, using a nearby quantum point contact (QPC) as a charge meter. The QPC is capacitively coupled to the dot, and the QPC conductance changes by about 1% if the number of electrons on the dot changes by one. The QPC is voltage biased and the current is monitored with an IV-convertor at room temperature. We can resolve tunnel events separated by only 8 $\\mu$s, limited by noise from the IV-convertor. Shot noise in the QPC sets a 25 ns lower bound on the accessible timescales.

  12. Electronic states and tunneling times in coupled self-assembled quantum dots

    Science.gov (United States)

    López-Bolaños, R.; Cocoletzi, G. H.; Ulloa, S. E.

    2001-11-01

    Electron energy levels in single dots, and energy splitting and tunneling times in stacked quantum dots are calculated as functions of structure parameters. An effective mass approach is used to solve the Schrödinger equation for cylindrical dots with finite confinement potentials. Strong confinement due to small sizes produces quantized energy levels in single dots and strong interactions of the wavefunctions with adjacent dots. This electronic coupling induces significant energy splittings and short tunneling times for characteristic structures used in experiments. This coupling may even yield coherent artificial molecular states with different optical properties.

  13. Real-time detection of single electron tunneling using a quantum point contact

    OpenAIRE

    Vandersypen, L.M.K.; Elzerman, J. M.; Schouten, R. N.; van Beveren, L. H. Willems; Hanson, R; Kouwenhoven, L.P.

    2004-01-01

    We observe individual tunnel events of a single electron between a quantum dot and a reservoir, using a nearby quantum point contact (QPC) as a charge meter. The QPC is capacitively coupled to the dot, and the QPC conductance changes by about 1% if the number of electrons on the dot changes by one. The QPC is voltage biased and the current is monitored with an IV-convertor at room temperature. We can resolve tunnel events separated by only 8 $\\mu$s, limited by noise from the...

  14. Probing the longitudinal momentum spread of the electron wave packet at the tunnel exit

    DEFF Research Database (Denmark)

    N. Pfeiffer, Adrian; Cirelli, Claudio

    2012-01-01

    We present an ellipticity resolved study of momentum distributions arising from strong-field ionization of Helium at constant intensity. The influence of the ion potential on the departing electron is considered within a semi-classical model consisting of an initial tunneling step and subsequent classical propagation. We find that the momentum distribution can be explained by the presence of a longitudinal momentum spread of the electron at the exit from the tunnel. Our combined experimental and theoretical study provides an estimate of this momentum spread.

  15. Probing the longitudinal momentum spread of the electron wave packet at the tunnel exit

    Directory of Open Access Journals (Sweden)

    Madsen Lars B.

    2013-03-01

    Full Text Available We present an ellipticity resolved study of momentum distribution arising from strong-field ionization of helium. The influence of the ion potential on the departing electron is considered within a semi-classical model consisting of an initial tunneling step and subsequent classical propagation. We find that the momentum distribution can be explained by including the longitudinal momentum spread of the electron at the exit from the tunnel. Our combined experimental and theoretical study provides an estimate of this momentum spread.

  16. Excitation of local magnetic moments by tunnelling electrons

    OpenAIRE

    Gauyacq, Jean-pierre; Lorente, Nicolas; Novaes, Frederico Dutilh

    2012-01-01

    The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These struct...

  17. Electron flux during pericyclic reactions in the tunneling limit: Quantum simulation for cyclooctatetraene

    Energy Technology Data Exchange (ETDEWEB)

    Hege, Hans-Christian [Abteilung Visualisierung und Datenanalyse, Zuse-Institut Berlin, Takustr. 9, 14195 Berlin (Germany); Manz, Joern, E-mail: jmanz@chemie.fu-berlin.de [Institut fuer Chemie und Biochemie, Freie Universitaet Berlin, Takustr. 3, 14195 Berlin (Germany); Marquardt, Falko [Abteilung Visualisierung und Datenanalyse, Zuse-Institut Berlin, Takustr. 9, 14195 Berlin (Germany); Institut fuer Mathematik, Freie Universitaet Berlin, Arnimallee 6, 14195 Berlin (Germany); Paulus, Beate; Schild, Axel [Institut fuer Chemie und Biochemie, Freie Universitaet Berlin, Takustr. 3, 14195 Berlin (Germany)

    2010-11-10

    Graphical abstract: In the limit of coherent tunneling, double bond shifting (DBS) of cyclooctatetraene from a reactant (R) to a product (P) is associated with pericyclic electron fluxes from double to single bonds, corresponding to a pincer-motion-type set of arrows in the Lewis structures, each representing a transfer of 0.19 electrons. - Abstract: Pericyclic rearrangement of cyclooctatetraene proceeds from equivalent sets of two reactants to two products. In the ideal limit of coherent tunneling, these reactants and products may tunnel to each other by ring inversions and by double bond shifting (DBS). We derive simple cosinusoidal or sinusoidal time evolutions of the bond-to-bond electron fluxes and yields during DBS, for the tunneling scenario. These overall yields and fluxes may be decomposed into various contributions for electrons in so called pericyclic, other valence, and core orbitals. Pericyclic orbitals are defined as the subset of valence orbitals which describe the changes of Lewis structures during the pericyclic reaction. The quantum dynamical results are compared with the traditional scheme of fluxes of electrons in pericyclic orbitals, as provided by arrows in Lewis structures.

  18. Scanning tunneling spectrum of electrons confined in a rectangular quantum corral

    International Nuclear Information System (INIS)

    We obtained the scanning tunneling spectrum (STS) of an electron confined in a rectangular quantum corral by considering the electron to be in a quasi-stationary state. Because of non-hermiticity of the Hamiltonian, the electron has a complex eigenenergy. The imaginary part gives the peak width coming mainly from the electron tunneling through a corral barrier. Our STS is consistent with the experimental spectrum that had been measured for electrons confined in a rectangular quantum corral. We obtained peak widths against energy levels and components of the STS which are constructed with quasi-stationary eigenstates. It is shown that normalization of a wavefunction by considering its time evolution is decisive in obtaining the proper STS. Moreover, we specified the position dependence of STS in relation to the image of the surface local density of states.

  19. Quantum theory of electron tunneling into intersubband cavity polariton states

    OpenAIRE

    De Liberato, Simone; Ciuti, Cristiano

    2009-01-01

    Through a non-perturbative quantum theory, we investigate how the quasi-electron excitations of a two-dimensional electron gas are modified by strong coupling to the vacuum field of a microcavity. We show that the electronic dressed states originate from a Fano-like coupling between the bare electron states and the continuum of intersubband cavity polariton excitations. In particular, we calculate the electron spectral function modified by light-matter interactions and its i...

  20. Band electron spectrum and thermodynamic properties of the pseudospin-electron model with tunneling splitting of levels

    Directory of Open Access Journals (Sweden)

    O.Ya.Farenyuk

    2006-01-01

    Full Text Available The pseudospin-electron model with tunneling splitting of levels is considered. Generalization of dynamic mean-field method for systems with correlated hopping was applied to the investigation of the model. Electron spectra, electron concentrations, average values of pseudospins and grand canonical potential were calculated within the alloy-analogy approximation. Electron spectrum and dependencies of the electron concentrations on chemical potential were obtained. It was shown that in the alloy-analogy approximation, the model possesses the first order phase transition to ferromagnetic state with the change of chemical potential and the second order phase transition with the change of temperature.

  1. Effect of ion-milled barriers on electron transport in micrometer-sized tunnel junctions

    International Nuclear Information System (INIS)

    We studied the electron transport properties of micrometre-sized all-Al tunnel junctions (TJs) between 2 and 300 K, in which the AlOx layer grown by O2 plasma was moderately Ar-ion-milled prior to top electrode deposition. In contrast to the direct tunnelling in the TJs whose barriers are intact (not ion-milled), the zero-bias conductances and the current–voltage characteristics of the TJs as processed are found to be best described by the fluctuation-induced tunnelling conduction mechanism. This observation indicates the formation of nanoscopic incomplete pinholes in the AlOx layer, owing to large junction–barrier interfacial roughness introduced by the ion-milling process. Topographical features revealed by the cross-sectional transmission electron microscopy imaging of the TJ stack conform to this result. This study is of relevance to cases in which ion-milling techniques are applied in tailoring the TJ properties. (paper)

  2. Enhancement of tunnel conductivity by Cooper pair fluctuations in electron-hole bilayer

    International Nuclear Information System (INIS)

    Influence of Cooper pair fluctuations that are precursor of pairing of electrons and holes located on opposite surfaces of topological insulator film on tunnel conductivity between the surfaces is investigated. Due to restrictions caused by momentum and energy conservation dependence of tunnel conductivity on external bias voltage has peak that becomes more prominent with decreasing of disorder and temperature. We have shown that Cooper pair fluctuations considerably enhance tunneling and height of the peak diverges in vicinity of critical temperature with critical index ? = 2. Width of the peak tends to zero in proximity of critical temperature. Pairing of electrons and holes can be suppressed by disorder and in vicinity of quantum critical point height of the peak also diverges as function of Cooper pair damping with critical index ? = 2.

  3. Negative differential resistance in electron tunneling in ultrathin films near the two-dimensional limit

    International Nuclear Information System (INIS)

    We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample bias voltage, at which negative differential resistance and peak negative conductance occur, depends on the film thickness. This can be understood from the variation in the LDOS of the Ag films as a function of film thickness down to the two-dimensional limit of one atomic layer. First principles density functional theory calculations have been used to explain the results.

  4. Electronic resource management systems a workflow approach

    CERN Document Server

    Anderson, Elsa K

    2014-01-01

    To get to the bottom of a successful approach to Electronic Resource Management (ERM), Anderson interviewed staff at 11 institutions about their ERM implementations. Among her conclusions, presented in this issue of Library Technology Reports, is that grasping the intricacies of your workflow-analyzing each step to reveal the gaps and problems-at the beginning is crucial to selecting and implementing an ERM.

  5. Electronic spectrum and tunnelling properties of multi-wall carbon nanotubes

    CERN Document Server

    Abrikosov, A A; Varlamov, A A

    2004-01-01

    We develop a general approach to calculations of the electron spectrum of metallic multi-wall carbon nanotubes (MWNT) with arbitrary number of coaxial layers. It is based on the model with singular attractive potential of equidistant conductive cylinders. The knowledge of one-electron spectrum allows to construct the corresponding Green function and then to calculate the entropy and density of states for MWNT. We analyze the tunnelling between the nanotube and normal metal electrode. The possibility of direct determination of one-electron density of states by measurements of the tunnelling conductivity at low temperatures is proved and the necessary restrictions on temperature are formulated. We discuss briefly the conflicting experimental observations of electronic properties of MWNT.

  6. Tunable few-electron double quantum dots and Klein tunnelling in ultraclean carbon nanotubes

    Science.gov (United States)

    Steele, G. A.; Gotz, G.; Kouwenhoven, L. P.

    2009-06-01

    Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies and research into new device applications. In particular, they have unique properties that make them attractive for studying the coherent properties of single-electron spins. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers, but disorder has prevented tunable nanotube-based quantum-dot devices from reaching the single-electron regime. Here, we use local gate voltages applied to an ultraclean suspended nanotube to confine a single electron in both a single quantum dot and, for the first time, in a tunable double quantum dot. This tunability is limited by a novel type of tunnelling that is analogous to the tunnelling in the Klein paradox of relativistic quantum mechanics.

  7. Tunnel and pnpn diodes in fast electronics for discrimination and counting devices in nuclear physics

    International Nuclear Information System (INIS)

    With a simple apparatus without power supply, the authors measured the rise time of the pulse produced by the fast switching of a tunnel diode. This time was of the order of 0.5 ns. The addition of a source of current made it possible to mount an ultra-fast amplitude-discrimination trigger working at a nanosecond. Problems of power supply and impedance adaptation make this a delicate experiment to perform successfully. It is particularly difficult to get good trigger threshold stability, as this is very sensitive to the supply voltage. At the present stage of the technique, a bi-stable flip-flop utilizing only one tunnel diode does not offer the operational security which would permit its use in nuclear physics. But it is possible to construct bi-stable flip-flops with two tunnel diodes. A system of n tunnel diodes in series, fed by a constant-current generator, presents n potential stable states. It is therefore possible to construct fast scalers of astonishing simplicity. Unfortunately, up until now zeroing has required the use of slower active or passive elements which do not allow full use to be made of the scaler's capacity. Combinations of tunnel diodes make it easy to construct rather complex electronic commutators. To conclude: the difficulty of using tunnel diode circuits lies essentially in problems of power feed and in linking them with other electronic gear. Nevertheless, their very considerable advantages justify intensive study in order to render them siintensive study in order to render them simpler to use. With four-layer diodes similar apparatus, but capable of furnishing considerable power, can be constructed. However, they require high voltages to justify their use in electronic tube circuits. (author)

  8. Temporal and spectral disentanglement of laser-driven electron tunneling emission from a solid

    OpenAIRE

    Yanagisawa, Hirofumi; Schnepp, Sascha; Hafner, Christian; Hengsberger, Matthias; Landsman, Alexandra; Gallmann, Lukas; Osterwalder, Juerg

    2014-01-01

    By measuring energy spectra of the electron emission from a sharp tungsten tip induced by few-cycle laser pulses, the laser-field dependence of the emission mechanism was investigated. In strong laser fields, we confirm the appearance of laser-driven tunneling emission and find that it can be disentangled from the concomitant photo-excited electron emission, both temporally and spectrally, by the opening of a peculiar emission channel. This channel involves prompt laser-driv...

  9. Tunneling images of a 2D electron system in a quantizing magnetic field

    CERN Document Server

    Maasilta, I J; Kuljanishvili, I; Tessmer, S H; Melloch, M R; Chakraborty, Subhasish

    2003-01-01

    We have applied a scanning probe method, Subsurface Charge Accumulation (SCA) imaging, to resolve the local structure of the interior of a semiconductor two-dimensional electron system (2DES) in a tunneling geometry. Near magnetic fields corresponding to integer Landau level filling, submicron scale spatial structure in the out-of-phase component of the tunneling signal becomes visible. In the images presented here, the structure repeats itself when the filling factor is changed from nu=6 to nu=7. Therefore, we believe the images reflect small modulations in the 2DES density caused by the disorder in the sample.

  10. Electron-acoustic phonon field induced tunnel scattering

    Directory of Open Access Journals (Sweden)

    S.V. Melkonyan

    2015-06-01

    Full Text Available Theory of electron-acoustic single phonon scattering has been reconsidered. It is assumed that the non-degenerate semiconductor has a spherical parabolic band structure. In the basis of the reconsideration there is a phenomenon of the tilting of semiconductor bands by the perturbing potential of an electric field. In this case, electron eigenfunctions are not plane waves or Bloch functions. In low-field regime, the expressions for electron intraband transition probability and scattering time are obtained under elastic collision approximation. Dependencies of scattering time on electron energy and uniform electric field are analyzed. The results of corresponding numerical computations for n-Si at 300 K are presented. It is established that there is no fracture on the curve of electron scattering time on the electron energy dependence.

  11. Quantum Tunneling Activity

    Science.gov (United States)

    This resource provides an introductory activity on the basics of quantum tunneling. As the activity states, "Real-world examples are given to demonstrate the importance of this effect to modern technologies." The activity covers concepts such as crossing a barrier both at the macroscopic and microscopic scale, tunneling leakage in computer chips, tunnel injection and release in flash memory and DNA sequencing. This module allows students to test their knowledge as they go. Although a preview of the activity is available, instructors and students are encouraged to sign up with the Electron Technologies site before starting to use these materials.

  12. Formation of hot electrons in noble gases by intense-field ionization: A quasistatic tunneling, independent-electron model

    International Nuclear Information System (INIS)

    Recent experiments by Mohideen et al. [Phys. Rev. Lett. 71, 509 (1993)] demonstrated that more hot electrons result from high-intensity above-threshold ionization of atoms than had been predicted by existing models. In this paper we explain most of the discrepancy between the theory and experimental data on the basis of a quasistatic tunneling independent-electron (QTIE) model, formulated using a simple set of rate equations with quasistatic expressions for ionization probabilities. Because of the efficiency of the QTIE approach, one can easily perform calculations of strong-field ionization for many-electron atoms. We demonstrate the properties of tunneling ionization in applications to He, Ne, Ar, Kr, and Xe

  13. Detecting stray microwaves and nonequilibrium quasiparticles in thin films by single-electron tunneling

    Science.gov (United States)

    Saira, Olli-Pentti; Maisi, Ville; Kemppinen, Antti; Möttönen, Mikko; Pekola, Jukka

    2013-03-01

    Superconducting thin films and tunnel junctions are the building blocks of many state-of-the-art technologies related to quantum information processing, microwave detection, and electronic amplification. These devices operate at millikelvin temperatures, and - in a naive picture - their fidelity metrics are expected to improve as the temperature is lowered. However, very often one finds in the experiment that the device performance levels off around 100-150 mK. In my presentation, I will address three common physical mechanisms that can cause such saturation: stray microwaves, nonequilibrium quasiparticles, and sub-gap quasiparticle states. The new experimental data I will present is based on a series of studies on quasiparticle transport in Coulomb-blockaded normal-insulator-superconductor tunnel junction devices. We have used a capacitively coupled SET electrometer to detect individual quasiparticle tunneling events in real time. We demonstrate the following record-low values for thin film aluminum: quasiparticle density nqp shielding.

  14. Electron tunneling from electronically excited states of isolated bisdisulizole-derived trianion chromophores following UV absorption.

    Science.gov (United States)

    Winghart, Marc-Oliver; Yang, Ji-Ping; Kühn, Michael; Unterreiner, Andreas-Neil; Wolf, Thomas J A; Dau, Phuong D; Liu, Hong-Tao; Huang, Dao-Ling; Klopper, Wim; Wang, Lai-Sheng; Kappes, Manfred M

    2013-05-14

    Photoelectron spectra of isolated [M-BDSZ](3-) (BDSZ = bisdisulizole, M = H, Li, Na, K, Cs) triply charged anions exhibit a dominant constant electron kinetic energy (KE) detachment feature, independent of detachment wavelengths over a wide UV range. Photoelectron imaging spectroscopy shows that this constant KE feature displays an angular distribution consistent with delayed rather than direct electron emission. Time-resolved pump-probe (388 nm/775 nm) two-colour photoelectron spectroscopy reveals that the constant KE feature results from two simultaneously populated excited states, which decay at different rates. The faster of the two rates is essentially the same for all the [M-BDSZ](3-) species, regardless of M. The slower process is associated with lifetimes ranging from several picoseconds to tens of picoseconds. The lighter the alkali cation is, the longer the lifetime of this state. Quantum chemical calculations indicate that the two decaying states are in fact the two lowest singlet excited states of the trianions. Each of the two corresponding photoexcitations is associated with significant charge transfer. However, electron density is transferred from different ends of the roughly chain-like molecule to its aromatic center. The energy (and therefore the decay rate) of the longer-lived excited state is found to be influenced by polarization effects due to the proximal alkali cation complexed to that end of the molecule. Systematic M-dependent geometry changes, mainly due to the size of the alkali cation, lead to M-dependent shifts in transition energies. At the constant pump wavelength this leads to different amounts of vibrational energy in the respective excited state, contributing to the variations in decay rates. The current experiments and calculations confirm excited state electron tunneling detachment (ESETD) to be the mechanism responsible for the observed constant KE feature. The ESETD phenomenon may be quite common for isolated multiply charged anions, which are strong fluorophores in the condensed phase - making ESETD useful for studies of the transient response of such species after electronic excitation. PMID:23549163

  15. Electron-phonon interaction in electronic tunneling: from sequential rate equations to a coherent description

    Scientific Electronic Library Online (English)

    L.E.F. Foa, Torres; H.M., Pastawski; S. S., Makler.

    2002-06-01

    Full Text Available We discuss the main theoretical approaches for the phonon-assisted tunneling in double barrier resonant tunneling devices and introduce a quantum coherent treatment based on the mapping of the many-body problem into a higher dimensional one-body system. Conditions for a maximized phonon-emission are [...] established.

  16. Spin-controlled nanomechanics induced by single-electron tunneling

    OpenAIRE

    Radic, Danko; Nordenfelt, Anders; Kadigrobov, Anatoli M.; Shekhter, Robert I.; Jonson, Mats; Gorelik, Leonid Y.

    2011-01-01

    We consider dc-electronic transport through a nanowire suspended between normal- and spin-polarized metal leads in the presence of an external magnetic field. We show that magnetomotive coupling between the electrical current through the nanowire and vibrations of the wire may result in self-excitation of mechanical vibrations. The self-excitation mechanism is based on correlations between the occupancy of the quantized electronic energy levels inside the nanowire and the velocity of the nano...

  17. Spin controlled nanomechanics induced by single-electron tunneling

    OpenAIRE

    Radic?, Danko; Nordenfelt, Anders; Kadigrobov, Anatoli M.; Shekhter, Robert I.; Jonson, Mats; Gorelik, Leonid Y.

    2011-01-01

    We consider dc-electronic transport through a nanowire suspended between normal- and spin-polarized metal leads in the presence of an external magnetic field. We show that magnetomotive coupling between the electrical current through the nanowire and vibrations of the wire may result in self excitation of mechanical vibrations. The self-excitation mechanism is based on correlations between the occupancy of the quantized electronic energy levels inside the nanowire and the ve...

  18. EETimes Network: The Worldwide Electronics Resource

    Science.gov (United States)

    2002-01-01

    EEdesign (last mentioned in the February 15, 2002 NSDL Report for Math, Engineering, and Technology is one of many Web sites that are part of the EETimes Network. This new resource for electrical engineering (EE) and electronics professionals integrates the online versions of global technical newspapers. It also serves as a central access point to sites for specific industries that are part of the EETimes Network. For instance, there are features for communications, analog design, embedded systems, semiconductors, and microwave engineering. All of this provides an excellent way to keep up to date on breakthrough technologies, market developments, and business dealings. This site is also reviewed in the August 16, 2002 Scout Report.

  19. Electron Tunneling Studies of Electron-Phonon Renormalization Effects in Indium.

    Science.gov (United States)

    Lai, Tzayshing Andrew

    Tunneling spectra produced by thick In films ((TURN)5 -40 (mu)m) backed by Al contain strong, damped oscillations due to Andreev scattering. Spectra are classifiable as simple, beat-modulated or complex. Complex spectra are rare and difficult to interpret. Beat-modulated spectra are more common ((TURN)25%), and simple spectra are the most common. We attribute modulated spectra to tunneling from two specific patches on the In Fermi surface. All simple spectra are attributed to just one of these patches. The known occurrence of two In fiber textures is probably responsible for this situation. Out view requires all modulated spectra to yield the same two velocities. It also requires all simple spectra to yield the same velocity, and that this value be degenerate with one of the others. We find that these conditions are satisfied. Our results justify analysis of a representative simple spectrum to obtain the complex renormalization, Z(E). Our ReZ(E)/Z(0) resembles the Rowell-McMillan result. Our hybrid estimates of McMillan's parameter are consistent with values predicted for second-zone holes, but not with third-zone electrons. Whereas theoretical fits to level locations yield reasonable results for ReZ(E), fits to amplitudes yield unexpected results for ImZ(E), and hence for (alpha)('2)F((omega)) which is inferred from ImZ(E). Briefly, levels just above the In gap are too strong relative to those that follow ---a feature common to all strong In spectra. We call this the low-bias amplitude anomaly. Concurrently, all strong In spectra exhibit a shoulder in dV/dI, which we call the dynamic resistance background anomaly. The two are almost certainly related since their narrow bias ranges coincide. We believe our ImZ(E) and (alpha)('2)F((omega)) results to be reliable at higher energies (2.5 -3.5 meV), where our ImZ(E) is only one-seventh the Rowell-McMillan value. Existing experimental results show that thinner Zn films (d(,N) films (d(,N) (GREATERTHEQ) 3 (mu)m), whereas both produce the same ImZ(,N)(E). Since Z(,N)(E) is analytic, ReZ(,N)(E) and ImZ(,N)(E) are Hilbert transforms of one another. We compute the transforms of ReZ(,N)(E) and EmZ(,N)(E), which we compare with their experimental counterparts. Thicker Zn films yield better internal agreement.

  20. Hysteresis loops of spin-dependent electronic current in a paramagnetic resonant tunnelling diode

    International Nuclear Information System (INIS)

    Nonlinear properties of the spin-dependent electronic transport through a semiconductor resonant tunnelling diode with a paramagnetic quantum well are considered. The spin-dependent Wigner–Poisson model of the electronic transport and the two-current Mott’s formula for the independent spin channels are applied to determine the current–voltage curves of the nanodevice. Two types of the electronic current hysteresis loops are found in the current–voltage characteristics for both the spin components of the electronic current. The physical interpretation of these two types of the electronic current hysteresis loops is given based on the analysis of the spin-dependent electron densities and the potential energy profiles. The differences between the current–voltage characteristics for both the spin components of the electronic current allow us to explore the changes of the spin polarization of the current for different electric fields and determine the influence of the electronic current hysteresis on the spin polarization of the current flowing through the paramagnetic resonant tunnelling diode. (paper)

  1. Probing hot-electron dynamics at surfaces with a cold scanning tunneling microscope

    OpenAIRE

    Burgi, L.; Jeandupeux, O.; Brune, H.; Kern, K.

    1999-01-01

    We report on a novel approach to measure the phase relaxation length and femtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interference patterns in the local density of states for surface state electrons on Ag(111) and Cu(111). This decay is governed by inelastic; electron-electron scattering. We find a (E - E-F)(-2) energy dependence of the lifetimes for both Ag and Cu, and our values are comparable t...

  2. The weak ? ? ? interaction originated resonant tunneling and fast switching in the carbon based electronic devices

    Directory of Open Access Journals (Sweden)

    Jun He

    2012-03-01

    Full Text Available By means of the nonequilibrium Green's functions and the density functional theory, we have investigated the electronic transport properties of C60 based electronic device with different intermolecular interactions. It is found that the electronic transport properties vary with the types of the interaction between two C60 molecules. A fast electrical switching behavior based on negative differential resistance has been found when two molecules are coupled by the weak ? ? ? interaction. Compared to the solid bonding, the weak interaction is found to induce resonant tunneling, which is responsible for the fast response to the applied electric field and hence the velocity of switching.

  3. The converse piezoelectric effect on electron tunnelling across a junction with a ferroelectric-ferromagnetic composite barrier

    Science.gov (United States)

    Wang, Jian; Ju, Sheng; Li, Z. Y.

    2010-04-01

    A theoretical investigation of the converse piezoelectric effect on electron tunnelling across a tunnel junction with a ferroelectric-ferromagnetic composite barrier is proposed. Transfer matrix calculations show that the spin filtering and tunnelling magnetoresistance may be enhanced or reduced due to the presence of converse piezoelectricity in the ferroelectric barrier, depending on the orientation of the electrical polarization in the barrier relative to the applied field. In addition, the tunnelling electroresistance is found to be significantly changed, not only in magnitude but also in sign. The investigation offers a new route towards controllable spin transport.

  4. The converse piezoelectric effect on electron tunnelling across a junction with a ferroelectric-ferromagnetic composite barrier

    International Nuclear Information System (INIS)

    A theoretical investigation of the converse piezoelectric effect on electron tunnelling across a tunnel junction with a ferroelectric-ferromagnetic composite barrier is proposed. Transfer matrix calculations show that the spin filtering and tunnelling magnetoresistance may be enhanced or reduced due to the presence of converse piezoelectricity in the ferroelectric barrier, depending on the orientation of the electrical polarization in the barrier relative to the applied field. In addition, the tunnelling electroresistance is found to be significantly changed, not only in magnitude but also in sign. The investigation offers a new route towards controllable spin transport.

  5. Spin-Controlled Nanomechanics Induced by Single-Electron Tunneling

    Science.gov (United States)

    Radi?, D.; Nordenfelt, A.; Kadigrobov, A. M.; Shekhter, R. I.; Jonson, M.; Gorelik, L. Y.

    2011-12-01

    We consider dc-electronic transport through a nanowire suspended between normal- and spin-polarized metal leads in the presence of an external magnetic field. We show that magnetomotive coupling between the electrical current through the nanowire and vibrations of the wire may result in self-excitation of mechanical vibrations. The self-excitation mechanism is based on correlations between the occupancy of the quantized electronic energy levels inside the nanowire and the velocity of the nanowire. We derive conditions for the occurrence of the instability and find stable regimes of mechanical oscillations.

  6. Single-electron tunneling in InP nanowires

    CERN Document Server

    De Franceschi, S; Bakkers, E P A M; Feiner, L F; Gurevich, L A; Kouwenhoven, Leo P

    2003-01-01

    We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor-liquid-solid process. Our InP wires are n-type doped with diameters in the 40-55 nm range and lengths of several microns. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 micron. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ~1 meV. We also demonstrate energy quantization resulting from the confinement in the wire.

  7. Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy

    OpenAIRE

    So?de, Hajo; Talirz, Leopold; Gro?ning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Mu?llen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2014-01-01

    Atomically precise armchair graphene nanoribbons of width $N=7$ (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis of energy-dependent standing wave patterns of finite length ribbons allows, by Fourier transformation, the direct extraction of the dispersion relation of frontier electronic states. Aided by density functional theory calculations, we assign the states to the valence band, the conduction band and the next empty band of 7...

  8. Quantum discreteness and fundamental 1/f noise in tunnel junctions, nano-composites and other many-electron systems

    OpenAIRE

    Kuzovlev, Yu. E.; Medvedev, Yu. V.; Grishin, A. M.

    2000-01-01

    It is shown, with citing tunnel junction as an example, that mutual interplay of electron quantum transfers in a conducting system can be the fast mechanism for generation fundamental low-frequency flicker conductance fluctuations (1/f noise) without composing Lorentzians. This effect is lost in a theory which neglects the actual discreteness of electron energy levels. The analytical estimates of fluctuations of tunnel conductance are obtained, and the strong 1/f-noise sensi...

  9. Electrically tunable spin filtering for electron tunneling between spin-resolved quantum Hall edge states and a quantum dot

    International Nuclear Information System (INIS)

    Spin filtering with electrically tunable efficiency is achieved for electron tunneling between a quantum dot and spin-resolved quantum Hall edge states by locally gating the two-dimensional electron gas (2DEG) leads near the tunnel junction to the dot. The local gating can change the potential gradient in the 2DEG and consequently the edge state separation. We use this technique to electrically control the ratio of the dot–edge state tunnel coupling between opposite spins and finally increase spin filtering efficiency up to 91%, the highest ever reported, by optimizing the local gating.

  10. Titanium Silicide Islands on Atomically Clean Si(100): Identifying Single Electron Tunneling Effects

    CERN Document Server

    Tedesco, Joseph L; Nemanich, Robert J; 10.1063/1.3437049

    2010-01-01

    Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (< 2 nm) on atomically clean Si(100) substrates followed by annealing to ~800 degrees C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET. Some of the islands formed are small enough (diameter < 10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did n...

  11. Electron transport through cubic InGaN/AlGaN resonant tunneling diodes

    Science.gov (United States)

    Yahyaoui, N.; Sfina, N.; Nasrallah, S. Abdi-Ben; Lazzari, J.-L.; Said, M.

    2014-12-01

    We theoretically study the electron transport through a resonant tunneling diode (RTD) based on strained AlxGa1-xN/In0.1Ga0.9N/AlxGa1-xN quantum wells embedded in relaxed n- Al0.15Ga0.85N/strained In0.1Ga0.9N emitter and collector. The aluminum composition in both injector and collector contacts is taken relatively weak; this does not preclude achieving a wide band offset at the border of the pre-confinement wells. The epilayers are assumed with a cubic crystal structure to reduce spontaneous and piezoelectric polarization effects. The resonant tunneling and the thermally activated transfer through the barriers are the two mechanisms of transport taken into account in the calculations based on the Schrödinger, Poisson and kinetic equations resolved self-consistently. Using the transfer matrix formalism, we have analyzed the influence of the double barrier height on the resonant current. With an Al composition in the barriers varying between 30% and 50%, we have found that resonant tunneling dominates over the transport mediated by the thermally activated charge transfer for low applied voltages. It is also found that the designed n-type InGaN/AlGaN RTD with 30% of Al composition in the barriers is a potential candidate for achieving a resonant tunneling diode.

  12. Massive Dirac electron tunneling through a time-periodic potential in single layer graphene

    International Nuclear Information System (INIS)

    We explore the transmission through a time-periodic potential barriers in single layer graphene with an induced energy gap in this work. The analytical solutions of the transmission probabilities for the central band and the first sidebands are obtained. The transmission probabilities as the function of the induced energy gap and the incidence electron energy are discussed. We also investigate how critical angles change as the induced energy gap and incidence electron energy. The study of transmission properties will benefit applications in graphene-based nano-electronics. -- Highlights: ? The tunneling of massive electrons through a harmonically driven potential barrier. ? Analytical solutions of transmission probabilities for the first sidebands. ? Adjusting energy gap and incidence energy will optimize transmission probabilities. ? Incidence critical angles change as energy gap and incidence electron energy.

  13. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  14. Zener Tunneling Between Landau Orbits in a High-Mobility Two-Dimensional Electron Gas

    CERN Document Server

    Yang, C L; Du, R R; Simmons, J A; Reno, J L

    2002-01-01

    Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs-AlGa$_{0.3}$As$_{0.7}$ heterostructures, and can be well explained by the Zener mechanism.

  15. Phonon-assisted tunneling of electrons in a quantum well/quantum dot injection structure

    Science.gov (United States)

    Mielnik-Pyszczorski, Adam; Gawarecki, Krzysztof; Machnikowski, Pawe?

    2015-05-01

    We study theoretically phonon-assisted relaxation and tunneling in a system composed of a quantum dot which is coupled to a quantum well. Within the k .p method combined with the Löwdin elimination, we calculate the electron states. We calculate acoustic phonon-assisted relaxation rates between the states in the quantum well and in the quantum dot and study the resulting electron kinetics. We show that transition efficiency crucially depends on the system geometry. We show also that under some conditions, transition efficiency can decrease with the temperature.

  16. Effects of intradot electron-electron interaction on the photon-assisted Andreev tunneling through a finite-sized carbon-nanotube system

    International Nuclear Information System (INIS)

    The effects of intradot electron-electron interaction on the photon-assisted Andreev tunneling of a superconductor/carbon-nanotube/superconductor system are studied by using nonequilibrium Green's function technique. The inverse supercurrent reflecting the ?-junction transition emerges in the spin-split energy-levels regime polarized by the Coulomb interaction. For the positive tunneling case, the supercurrent reaches its maximum when the spin-degenerate energy-levels are nearest to the Fermi surface. Conversely, for the negative tunneling case, the supercurrent reaches its maximum when two split energy-levels are symmetric with respect of the Fermi surface. The sign and the amplitude of the Andreev tunneling depend distinctly on the energy-level spacing tuned by photon-assisted tunneling. In order to fully understand the transport characteristics, the current-carrying density of states are investigated, which clearly shows the enhancement, suppression or even reversion of the supercurrent

  17. Negative differential resistance at sequential single-electron tunnelling through atoms and molecules

    International Nuclear Information System (INIS)

    We have carried out calculations of electron transport in single-electron transistors using single atoms or small molecules as single-electron islands. The theory is based on a combination of (i) the general theory of the sequential single-electron transport through objects with a quantized energy spectrum, developed by Averin and Korotkov, (ii) the ab initio calculation of molecular orbitals and energy spectra within the density functional theory framework (using the NRLMOL software package), and (iii) Bardeen's approximation for the rate of tunnelling due to wavefunction overlap. The results show, in particular, that dc I-V curves of molecular-scale single-electron transistors typically have extended branches with negative differential resistance. This effect is due to the enhancement of one of the two tunnelling barriers of the transistor by the source-drain electric field, and apparently has already been observed experimentally by at least two groups. In conclusion, the possibility of using this effect for increasing the density and performance of hybrid semiconductor/nanodevice integrated circuits is discussed in brief

  18. Single-molecule electron tunnelling through multiple redox levels with environmental relaxation

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2004-01-01

    We present an analytical theory for electron flow through a molecule with several redox levels, enclosed between a pair of metallic electrodes. The levels can be electronic or electronic-vibrational levels. Vibrational energy spacing characterises the latter sets. The levels are further coupled to environmental nuclear motion. Cryogenic temperatures are considered. This implies that thermal activation is disregarded but vibrational relaxation in the molecular charge states is central. The electrochemical potentials of the electrodes are controlled relative to a reference electrode. The electrodes represent the substrate and tip in electrochemical in situ scanning tunnelling microscopy. An equivalent three-electrode configuration represents a molecular single-electron transistor in which the enclosing electrodes constitute source and drain, and the reference electrode the gate. Current-bias voltage relations at fixed electrochemical overpotential or gate voltage, and current-overpotential or current-gate voltage relations at fixed bias voltage are equivalent in the two systems. Due to the activation-less nature of the processes, electron flow between the electrodes through the molecular redox levels can be only achieved when the latter are located between the Fermi levels of the substrate and tip or source and drain electrodes. The redox levels can be brought into this "energy window", either by the overpotential or bias and gate voltages, or by vibrational relaxation of (a) given (set of) redox level(s) subsequent to electron transfer. Several physical mechanisms can be distinguished and distinctive current-overpotential/gate voltage or current-bias voltage relations obtained. These reflect electronic level separation, environmental nuclear reorganisation, and coherent or incoherent multi-electron flow. The models and formalism have bearings on construction of single-molecule devices, illustrated by a short discussion of single-electron tunnelling in semiconductor quantum dots and reported low-temperature single-molecular transistor effects.

  19. Nonlocal and Quantum Tunneling Contributions to Harmonic Generation in Nanostructures: Electron Cloud Screening Effects

    CERN Document Server

    Scalora, Michael; de Ceglia, Domenico; Haus, Joseph W

    2014-01-01

    Our theoretical examination of second and third harmonic generation from metal-based nanostructures predicts that nonlocal and quantum tunneling phenomena can significantly exceed expectations based solely on local, classical electromagnetism. Mindful that the diameter of typical transition metal atoms is approximately 3{\\AA}, we adopt a theoretical model that treats nanometer-size features and/or sub-nanometer size gaps or spacers by taking into account: (i) the limits imposed by atomic size to fulfill the requirements of continuum electrodynamics; (ii) spillage of the nearly-free electron cloud into the surrounding vacuum; and (iii) the increased probability of quantum tunneling as objects are placed in close proximity. Our approach also includes the treatment of bound charges, which add crucial, dynamical components to the dielectric constant that are neglected in the conventional hydrodynamic model, especially in the visible and UV ranges, where interband transitions are important. The model attempts to i...

  20. Electron tunneling study of the superconducting proximity effect in Pb-Cd

    International Nuclear Information System (INIS)

    Electron tunneling has been used to study the superconducting state in superimposed Pb-Cd thin films in which the Pb thickness varied from 950 to 330 A. The measured transition temperature T/sub c/ varied from 7.22 to 4.86 K in the samples, and the observed energy gaps varied from 1.38 to 0.43 meV. The tunneling density of states as recorded on either side of the sandwich resembles those predicted by the McMillan model, but there are some quantitative differences. The observed phonon structure in the density of states occurs at the same energy as that in bulk Pb, and the magnitude of the structure scales with T2/sub c/. The shape of the calculated phonon spectral function remains essentially unchanged throughout this series

  1. Estimation of the radiation dose to the electronic equipment inside the B - factory ring tunnel

    International Nuclear Information System (INIS)

    The B - factory is a new, future high energy physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a positron ring (4 GeV, called LER) atop an electron ring ( 10 GeV, called HER). Both rings have a circulating current of 3 A, corresponding to a beam particle number of 1.38 x 10 sup 1 sup 4. Interest was expressed to place electronic equipment inside the tunnel for cost reasons. Estimation of the radiation dose that may damage the electronics was therefore made at a few locations. An analytical SHIELD 11 code was used to calculate the dose from high energy photon and neutron radiation resulting from various beam loss scenarios, which include normal stored beam, injection and unusual operations. The EGS4 Monte Carlo code was used to calculate the dose from the synchrotron radiation escaping the vacuum chambers. The synchrotron radiation doses from two different LER designs were studied : a 0.35 cm thick copper wall vacuum chamber and a 1 cm thick aluminum chamber with a copper mask 6 m downstream of the bending magnet to absorb the synchrotron radiation locally. The HER design was a 0.5 cm thick copper chamber. No bending magnet structure shielding was assumed for LER while a C - shape iron bending magnet was used for HER. In addition, the dose from the radiation ( photon, neutron, and synchrotron radiation) scattering back from the concrete tunnel wall was also estimated with albedo method, which was derived from the MORSE runthod, which was derived from the MORSE runs. The results showed that a location between the HER and the floor has a dose level of 3 Gy y sup -1 , which makes it the most suitable location for the electronic equipment with a damage threshold of Gy y sup-1. Other results and discussions will be given. 1 fig; 2 tabs; 2 refs (author)

  2. Inelastic electron tunneling spectroscopy of CoFeB/ MgO/ CoFeB based magnetic tunnel junctions in high magnetic fields

    International Nuclear Information System (INIS)

    Magnetic tunnel junctions (MTJs) showing a high tunnel magnetoresistance (TMR) are important for the fabrication of MRAM devices when combined with current induced switching. We discuss inelastic electron tunneling spectroscopy (IETS) measurements on CoFeB/MgO/CoFeB magnetic tunnel junctions. The junctions are prepared by means of magnetron sputtering of CoFeB and e-beam evaporation of stoichiometric MgO. Structuring of the multilayer is done using a photolithography process and Argon ion-milling. The IETS measurements are carried out at low temperatures down to 4.2 K, high magnetic fields up to 9 T and in parallel as well as antiparallel electrode configuration in order to distinguish between different kind of excitations such as e.g. magnons and phonons. Furthermore, oxygen vacancies in the MgO barrier are controlled through variation of the sample temperature during e-beam growth to investigate the influences of these vacancies on the tunneling spectra of MTJs.

  3. Assessment of field-induced quantum confinement in heterogate germanium electron–hole bilayer tunnel field-effect transistor

    International Nuclear Information System (INIS)

    The analysis of quantum mechanical confinement in recent germanium electron–hole bilayer tunnel field-effect transistors has been shown to substantially affect the band-to-band tunneling (BTBT) mechanism between electron and hole inversion layers that constitutes the operating principle of these devices. The vertical electric field that appears across the intrinsic semiconductor to give rise to the bilayer configuration makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, therefore increasing the effective bandgap close to the gates and reducing the BTBT probabilities. In this letter, we present a simulation approach that shows how the inclusion of quantum confinement and the subsequent modification of the band profile results in the appearance of lateral tunneling to the underlap regions that greatly degrades the subthreshold swing of these devices. To overcome this drawback imposed by confinement, we propose an heterogate configuration that proves to suppress this parasitic tunneling and enhances the device performance.

  4. Proximity effect and hot-electron diffusion in Ag/Al2O3/Al tunnel junctions

    International Nuclear Information System (INIS)

    We have fabricated Ag/Al2O3/Al tunnel junctions on Si substrates using a new process. This process was developed to fabricate superconducting tunnel junctions (STJs) on the surface of a superconductor. These junctions allow us to study the proximity effect of a superconducting Al film on a normal metal trapping layer. In addition, these devices allow us to measure the hot-electron diffusion constant using a single junction. Lastly these devices will help us optimize the design and fabrication of tunnel junctions on the surface of high-Z, ultra-pure superconducting crystals. 5 refs., 8 figs

  5. Electron tunneling characteristics of a cubic quantum dot, (PbS)32

    International Nuclear Information System (INIS)

    The electron transport properties of the cubic quantum dot, (PbS)32, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (?2 eV), a relatively high tunneling current for (PbS)32 is predicted affirming the observed bright images for (PbS)32. The calculated I-V characteristics of (PbS)32 are predicted to be substrate-dependent; (PbS)32 on the Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS)32 on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system

  6. Numerical investigation of tunnelling contributions to electron scavenging reactions in liquids at short times

    International Nuclear Information System (INIS)

    Fick's second diffusion equation, with an added exponential sink term, is integrated numerically to simulate the decay of electrons at short times in the presence of scavengers. The time dependence of the scavenger concentration profile, the scavenging rate constant, and the electron concentration are illustrated graphically. Using the experimental results of Buxton et al. and Jonah et al., it is shown that the Smoluchowski equation is valid within their experimental time ranges provided the cage encounter distance is replaced by Rsub(eff), where Rsub(eff) can be evaluated explicitly in terms of reaction parameters. It is also shown that tunnelling from relaxed traps may make a significant contribution to ultra-short time electron scavenging. (author)

  7. Correlation - Function Analysis of Coupled Electron - Phonon Systems: Signatures of Polaron Tunneling

    International Nuclear Information System (INIS)

    Intrinsic 'local textures' are becoming a leitmotiv of complex electronic materials, including high-Tc superconductors. Here we discuss signatures of nonlinear dynamics in the context of small polarons through various correlation functions which measure correlated structural and optical properties of a system. It is shown that energy-resolved correlation functions can be used to probe length and time scales in a unique fashion. These methods are applied to a polaron-tunneling problem which not only serves as a prototype for nonlinear and nonadiabatic behaviour in the presence of coupled electronic and lattice degrees of freedom, but may also be relevant to discraibing aspects of local electronic and structural dynamics in high-Tc superconducting materials. (author)

  8. Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

    CERN Document Server

    Preisinger, M; Rudolf, T; Horn, S; Strongin, D R

    2005-01-01

    We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.

  9. Scanning tunnel microscopic image of tungsten (100) and (110) real surfaces and nature of conduction electron reflection

    International Nuclear Information System (INIS)

    The electrically polished (100) and (110) surfaces of tungsten are studied with the aid of a scanning tunnel microscope at atmospheric pressure. The (110) surface consists of a large number of atomically plane terraces whereas the (100) surface is faceted. The scanning tunnel microscope data can explain such results of experiments on transverse electron focussing as the strong dependence of the probability for specular reflection of conduction electrons scattered by the (100) surface on the electron de Broglie wavelength and the absence of a dependence of the probability for specular reflection on the wavelength for the (110) surface

  10. Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

    International Nuclear Information System (INIS)

    Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data

  11. Transverse Pseudospin Susceptibility and Tunneling Parameters of Double Layer Electron Gas Systems

    CERN Document Server

    Swierkowski, L

    1996-01-01

    The subbands of weakly coupled double-layer two dimensional electron gas systems consist of narrowly spaced pairs whose corresponding wavefunctions are symmetric and antisymmetric combinations of isolated layer subband wavefunctions. The energetic spacing within a pair is 2t where t is the interlayer tunneling amplitude. t is an important parameter in modeling these systems and, if interactions could be neglected, it would be proportional to beating frequencies seen in weak-field magnetic oscillations experiments and therefore readily measurable. We point out that interactions alter the beating frequency. We discuss similarities and differences between this effect and exchange-correlation enhanced spin-splitting.

  12. Transport of electrons in the tunnel of an ion sensitive probe.

    Czech Academy of Sciences Publication Activity Database

    Komm, Michael; Adámek, Ji?í; Dejarnac, Renaud; Gunn, J. P.; Pekárek, Z.

    2011-01-01

    Ro?. 53, ?. 1 (2011), 015005-015005. ISSN 0741-3335 R&D Projects: GA AV ?R KJB100430901; GA MŠk 7G09042; GA MŠk LA08048 Institutional research plan: CEZ:AV0Z20430508 Keywords : Tokamak * plasma * katsumata probe * ExB drift * ion temperature * tunnel * electron Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.425, year: 2011 http://iopscience.iop.org/0741-3335/53/1/015005/pdf/0741-3335_53_1_015005.pdf

  13. Improved model for the stress-induced leakage current in thin silicon dioxide based on conduction-band electron and valence-band electron tunneling

    Science.gov (United States)

    Chim, W. K.; Lim, P. S.

    2002-02-01

    This article presents a detailed investigation on the stress-induced leakage current (SILC) conduction mechanism via conduction-band electron (CBE) and valence-band electron (VBE) tunneling in thin oxides. An improved SILC model that is able to reproduce the experimental SILC over a wide range of oxide fields, and yet give a realistic level of extracted neutral trap concentration, is proposed. Calculations performed with the improved SILC model suggest that SILC conduction via neutral traps is accompanied by energy relaxation (i.e., an inelastic mechanism), irrespective of the origin (i.e., whether CBE or VBE) of the tunneling species. For both CBE and VBE tunneling, inelastic tunneling with energy relaxation (Erelax) of 1.5 and 0.8 eV, was found to fit the experimental measurements well. These values of Erelax agree with those reported in the literature.

  14. Using Electronic Resources to Support Problem-Based Learning

    Science.gov (United States)

    Chang, Chen-Chi; Jong, Ay; Huang, Fu-Chang

    2012-01-01

    Students acquire skills in problem solving and critical thinking through the process as well as team work on problem-based learning courses. Many courses have started to involve the online learning environment and integrate these courses with electronic resources. Teachers use electronic resources in their classes. To overcome the problem of the…

  15. The Role of the Acquisitions Librarian in Electronic Resources Management

    Science.gov (United States)

    Pomerantz, Sarah B.

    2010-01-01

    With the ongoing shift to electronic formats for library resources, acquisitions librarians, like the rest of the profession, must adapt to the rapidly changing landscape of electronic resources by keeping up with trends and mastering new skills related to digital publishing, technology, and licensing. The author sought to know what roles…

  16. Uncovering a law of corresponding states for electron tunneling in molecular junctions

    Science.gov (United States)

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C. Daniel

    2015-06-01

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible.Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02225h

  17. Quantum Tunneling

    Science.gov (United States)

    The Concord Consortium

    2011-12-11

    Delve into a microscopic world working with models that show how electron waves can tunnel through certain types of barriers. Learn about the novel devices and apparatuses that have been invented using this concept. Discover how tunneling makes it possible for computers to run faster and for scientists to look more deeply into the microscopic world.

  18. Incorporation of electron tunnelling phenomenon into 3D Monte Carlo simulation of electrical percolation in graphite nanoplatelet composites

    International Nuclear Information System (INIS)

    The percolation threshold problem in insulating polymers filled with exfoliated conductive graphite nanoplatelets (GNPs) is re-examined in this 3D Monte Carlo simulation study. GNPs are modelled as solid discs wrapped by electrically conductive layers of certain thickness which represent half of the electron tunnelling distance. Two scenarios of 'impenetrable' and 'penetrable' GNPs are implemented in the simulations. The percolation thresholds for both scenarios are plotted versus the electron tunnelling distance for various GNP thicknesses. The assumption of successful dispersion and exfoliation, and the incorporation of the electron tunnelling phenomenon in the impenetrable simulations suggest that the simulated percolation thresholds are lower bounds for any experimental study. Finally, the simulation results are discussed and compared with other experimental studies.

  19. Bulletin of entomological research [electronic resource].

    International Nuclear Information System (INIS)

    A journal covering agricultural entomology, medical and veterinary entomology, biological control, stored products entomology, and natural resource management. Includes taxonomic papers when relevant.

  20. Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique

    OpenAIRE

    Scherer, H.; Weimann, Th; Hinze, P.; Samwer, B. W.; Zorin, A. B.; Niemeyer, J.

    1999-01-01

    We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr tunnel junctions and SET transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x 60 nm^2 using a sc...

  1. Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure

    Energy Technology Data Exchange (ETDEWEB)

    Guo, P.; Yu, G. Q.; Wei, H. X.; Han, X. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, D. L.; Feng, J. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Kurt, H. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Department of Engineering Physics, Istanbul Medeniyet University, 34720 Istanbul (Turkey); Chen, J. Y.; Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

    2014-10-21

    Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4?mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d{sup 2}I/dV{sup 2}, and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy E{sub C} derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

  2. Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure

    International Nuclear Information System (INIS)

    Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4?mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d2I/dV2, and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy EC derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

  3. Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure

    Science.gov (United States)

    Guo, P.; Li, D. L.; Feng, J. F.; Kurt, H.; Yu, G. Q.; Chen, J. Y.; Wei, H. X.; Coey, J. M. D.; Han, X. F.

    2014-10-01

    Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4 mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d2I/dV2, and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy EC derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

  4. Quantum electron tunneling in flavin-porphyrin hetero-type Langmuir-Blodgett films

    Energy Technology Data Exchange (ETDEWEB)

    Isoda, Satoru; Akiyama, Kouichi; Nishikawa, Satoshi; Ueyama, Satoshi; Miyasaka, Hiroshi; Okada, Tadashi

    2004-11-01

    Photo-induced electron transfer in flavin-porphyrin hetero-type Langmuir-Blodgett (LB) films and its temperature dependence were investigated by means of the photocurrent measurements and the transient fluorometry. From 10 K to room temperature, transient photocurrent in sub-nanosecond time region was found to be independent of the temperature for a metal-insulator-metal device composed of the hetero-type LB films with a flavin-porphyrin molecular heterojunction (MHJ). This transient photocurrent was attributed to the charge separation (CS) process from the photo-excited flavin to the porphyryin at the MHJ on the basis of the temperature dependence of the fluorescence decay profiles of the excited flavin. By integrating these results with UV-visible absorption spectra, it was deduced that the fast temperature-independent CS process at the flavin-porphyrin MHJ was mainly due to the quantum electron tunneling regulated by high-frequency quantum modes of intramolecular vibrations.

  5. Modification of a Scanning Tunneling Microscope for Measurement of Ballistic Electron Emission Microscopy

    Science.gov (United States)

    Hsieh, Satcher; Hong, Jeongmin; Bokor, Jeffrey

    2014-03-01

    Magnetic memory and logic devices show great promise for integration with, and even replacement of, conventional complementary metal-oxide-semiconductor (CMOS) architectures. In order to characterize materials and deposition techniques for these devices, ballistic electron emission microscopy (BEEM) is used. BEEM is a spatially resolved metrological tool most commonly used for subsurface interface structures at the nanometer scale. We modify a scanning tunneling microscope (STM) to perform BEEM measurement via design and fabrication of a novel sample stage. Furthermore, we design and fabricate an external magnetic field source that encapsulates the sample stage, setting the foundation for future measurement of ballistic electron magnetic microscopy (BEMM). Instrumentation of the device and characterization of a sample with an ohmic interface, Ni-Si, are implemented and discussed. With support from National Science Foundation Award ECCS-0939514.

  6. Electronic structure properties of the In(Ga)As/GaAs quantum dot–quantum well tunnel-injection system

    International Nuclear Information System (INIS)

    We report on the electronic properties of GaAs-substrate-based structures designed as a tunnel-injection system composed of self-assembled InAs quantum dots and an In0.3Ga0.7As quantum well separated by a GaAs barrier. We have performed photoluminescence and photoreflectance measurements which have allowed the determination of the optical transitions in the QW–QD tunnel structure and its respective references with just quantum dots or a quantum well. The effective mass calculations of the band structure dependence on the tunnelling barrier thickness have shown that in spite of an expected significant tunnelling between both parts of the system, its strong asymmetry and the strain distribution cause that the quantum-mechanical-coupling-induced energy shift of the optical transitions is almost negligible for the lowest energy states and weakly sensitive to the width of the barrier, which finds confirmation in the existing experimental data

  7. D-Lib magazine [electronic resource].

    International Nuclear Information System (INIS)

    Presents "D-Lib Magazine," a monthly electronic publication related to digital libraries. Includes commentaries and news articles. Offers an archive of back issues and a site search engine. Provides access to working groups, digital library research

  8. Marketing of Electronic Resources in IIT Libraries

    Directory of Open Access Journals (Sweden)

    Daulat Jotwani

    2014-03-01

    Full Text Available Indian Institute of Technology (IIT libraries at Bombay, Delhi, Guwahati, Kanpur, Kharagpur, Madras, and Roorkee have been subscribing to over 15000 e-journals, e-books, databases, and other e-resources either individually or in consortia mode and spending a substantial part of their acquisition budget for over a decade now. This paper attempts to study the marketing efforts being made by these libraries to improve the awareness and increase the usage of these resources. Marketing-related data were collected through a questionnaire, personal visits, and discussions with the librarians, and the usage data were obtained from publishers. Data analysis revealed that e-resources in all IITs are being heavily used as the number of downloads have increased from 32,33,818 to 75,23,371 reflecting a growth of 132 % over a period of 9 years. The IIT libraries adopt multipronged approach and use 27 marketing techniques to promote their resources. The study also showed that there were downward fluctuations in usage in different years. It is suggested that these libraries shall regularly re-look at the marketing strategies and techniques; study their impact on the awareness and usage of the e-resources; identify and remove the bottlenecks; and make additional efforts including interacting with the users to ensure optimum utilisation of these resources.

  9. Radiation tolerant nuclear electric cell [electronic resource

    International Nuclear Information System (INIS)

    An electric cell comprises layers of moderating material 1 &8, nuclear fuel 2 &7, cathode 3, anode 6, and semiconductor junction layers 4 &5 adjacently stacked one above another. Ionic compounds with high proton numbers are used to form the semiconductor junction layers 4 &5. Highly energetic heavy ion daughter nuclides from the nuclear fuel layers 2 &7 penetrate into the semiconductor junction layers 4 &5. The collision of heavy ions with the valence band electrons in the semiconductor junction layers 4 &5 creates electron-hole pairs which provide electricity. If the semiconductor junction layers 4 &5 are fissile, then the nuclear fuel layers 2 &7 can be removed.

  10. Contribution of the metal/SiO2 interface potential to photoinduced switching in molecular single-electron tunneling junctions

    International Nuclear Information System (INIS)

    Photoinduced switching of the Coulomb staircase in molecular single-electron tunneling junctions was previously observed. These junctions consisted of evaporated SiO2 insulator (?5 nm), with tetrakis-3,5-di-t-butylphenyl-porphyrin (H2-TBPP) molecules as Coulomb islands, sandwiched between top and bottom electrodes. The reversible response and the relaxation time of the photoinduced switching suggest that this phenomenon depends on the properties of the metal/SiO2 interface rather than those of the H2-TBPP molecule or SiO2 tunneling layer. We analyzed the photoinduced switching according to the theory of single-electron tunneling taking into account the discrete molecular energy states and the metal/SiO2 interfacial electrostatic phenomena. We conclude that the main contributor to the photoinduced shift was the electrostatic potential formed through the space-charge exchange at the metal/SiO2 interface

  11. Uncovering a law of corresponding states for electron tunneling in molecular junctions.

    Science.gov (United States)

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C Daniel

    2015-06-01

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible. PMID:26008991

  12. Improving Electronic Resources through Holistic Budgeting

    Science.gov (United States)

    Kusik, James P.; Vargas, Mark A.

    2009-01-01

    To establish a more direct link between its collections and the educational goals of Saint Xavier University, the Byrne Memorial Library has adopted a "holistic" approach to collection development. This article examines how traditional budget practices influenced the library's selection of resources and describes how holistic collection…

  13. Electronic neural network for dynamic resource allocation

    Science.gov (United States)

    Thakoor, A. P.; Eberhardt, S. P.; Daud, T.

    1991-01-01

    A VLSI implementable neural network architecture for dynamic assignment is presented. The resource allocation problems involve assigning members of one set (e.g. resources) to those of another (e.g. consumers) such that the global 'cost' of the associations is minimized. The network consists of a matrix of sigmoidal processing elements (neurons), where the rows of the matrix represent resources and columns represent consumers. Unlike previous neural implementations, however, association costs are applied directly to the neurons, reducing connectivity of the network to VLSI-compatible 0 (number of neurons). Each row (and column) has an additional neuron associated with it to independently oversee activations of all the neurons in each row (and each column), providing a programmable 'k-winner-take-all' function. This function simultaneously enforces blocking (excitatory/inhibitory) constraints during convergence to control the number of active elements in each row and column within desired boundary conditions. Simulations show that the network, when implemented in fully parallel VLSI hardware, offers optimal (or near-optimal) solutions within only a fraction of a millisecond, for problems up to 128 resources and 128 consumers, orders of magnitude faster than conventional computing or heuristic search methods.

  14. Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors

    Science.gov (United States)

    Aghili Yajadda, Mir Massoud

    2014-10-01

    We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300 K) at low and high DC bias voltages (0.001 mV-50 V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.

  15. Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors

    Energy Technology Data Exchange (ETDEWEB)

    Aghili Yajadda, Mir Massoud [CSIRO Manufacturing Flagship, P.O. Box 218, Lindfield NSW 2070 (Australia)

    2014-10-21

    We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300 K) at low and high DC bias voltages (0.001 mV–50 V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.

  16. Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors

    International Nuclear Information System (INIS)

    We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300?K) at low and high DC bias voltages (0.001?mV–50?V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.

  17. Transverse electron momentum distribution in tunneling and over the barrier ionization by laser pulses with varying ellipticity

    CERN Document Server

    Ivanov, I A; Calvert, J E; Goodall, S; Wang, X; Xu, Han; Palmer, A J; Kielpinski, D; Litvinyuk, I V; Sang, R T

    2015-01-01

    We study transverse electron momentum distribution (TEMD) in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, both experimentally and theoretically, that the TEMD in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases.

  18. Electronics Learning-Resources on the Web

    Science.gov (United States)

    Williams, Charles D. H.

    The links on this page are to background information which students taking electronics courses (particularly PHY2003, PHY3128) may find helpful. The descriptors used in the tables are explained at the bottom of the page. Topics include Circuit Analysis and Complex Variables, Techniques and Good Practice, Oscilloscopes, Passive Components, Diodes, Transistors, Op-Amps, Filters, Digital Signal, Processing, Applications and Circuits, Monostables and Astables, and Microcontrollers and PICsSpice: Learning and using Spice

  19. Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting

    Science.gov (United States)

    Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

    2015-03-01

    Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

  20. Long-range electron tunnelling in oligo-porphyrin molecular wires

    Science.gov (United States)

    Sedghi, Gita; García-Suárez, Víctor M.; Esdaile, Louisa J.; Anderson, Harry L.; Lambert, Colin J.; Martín, Santiago; Bethell, Donald; Higgins, Simon J.; Elliott, Martin; Bennett, Neil; MacDonald, J. Emyr; Nichols, Richard J.

    2011-08-01

    Short chains of porphyrin molecules can mediate electron transport over distances as long as 5-10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction.

  1. A New XOR Structure Based on Resonant-Tunneling High Electron Mobility Transistor

    Directory of Open Access Journals (Sweden)

    Mohammad Javad Sharifi

    2009-01-01

    Full Text Available A new structure for an exclusive-OR (XOR gate based on the resonant-tunneling high electron mobility transistor (RTHEMT is introduced which comprises only an RTHEMT and two FETs. Calculations are done by utilizing a new subcircuit model for simulating the RTHEMT in the SPICE simulator. Details of the design, input, and output values and margins, delay of each transition, maximum operating frequency, static and dynamic power dissipations of the new structure are discussed and calculated and the performance is compared with other XOR gates which confirm that the presented structure has a high performance. Furthermore, to the best of authors' knowledge, it has the least component count in comparison to the existing structures.

  2. An XPS investigation of alumina thin films utilized in inelastic electron tunneling spectroscopy

    International Nuclear Information System (INIS)

    X-ray photoelectron spectroscopy (XPS) has been applied to characterize a number of different aluminium oxide (alumina) thin films utilized in inelastic electron tunneling spectrocopy (IETS). Since IETS has been found to be an effective means for obtaining vibrational information on catalytic systems, reliable means of clarifying the exact relationship between the IET thin film model catalysts and high surface area commercial aluminas are of considerable importance. XPS data might profitably provide such a means of comparison, although sufficiently reliable XPS data for commercial samples are not currently available. The various thin film aluminas are characterized as to their chemical nature, chemical state distributions, and relative oxygen-to-alumina concentration ratios by analysis of peak positions, peak widths and peak intensities, respectively. Moreover, effects due to heating and halogenating the surface have been investigated independently, since these are commonly utilized to enhance the catalytic behavior of commercial aluminas. (orig.)

  3. Surface acoustic wave induced electron tunneling from an InGaAs/GaAs wetting layer

    Energy Technology Data Exchange (ETDEWEB)

    Pustiowski, Jens; Schuelein, Florian J.R.; Wixforth, Achim; Krenner, Hubert J. [Lehrstuhl fuer Experimentalphysik I, Universitaet Augsburg, 86159 Augsburg (Germany); Reuter, Dirk; Wieck, Andreas D. [Lehrstuhl fuer Angewandte Festkoerperphysik, 44780 Bochum (Germany); Bichler, Max; Mueller, Kai; Finley, John J. [Walter-Schottky-Institut, 85748 Garching (Germany)

    2011-07-01

    We report on a stroboscopic technique to probe the dynamic modulation controlled by a surface acoustic wave (SAW) of the photoluminescence (PL) of a wetting layer which is formed during the growth of InGaAs/GaAs quantum dots. A short laser pulse ({tau} <100 ps) is actively phase locked to the frequency of the SAW and the relative phase between laser excitation and SAW can be precisely controlled. Thus, we are able to map one complete cycle of the SAW and study the PL quenching and its modulation in the time domain. For low SAW powers the observed modulation with the fundamental period of the SAW arises from different mobilities of electrons and holes. This imbalance leads to different ionization efficiencies in the type-II band gap modulation induced by the SAW. At high SAW power levels, the modulation period doubles which can be readily explained by SAW induced tunneling induced by the vertical piezoelectric field component.

  4. Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

    Energy Technology Data Exchange (ETDEWEB)

    Tsang, Juine Kai

    1980-01-01

    Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data.

  5. Transport of electrons in the tunnel of an ion sensitive probe

    International Nuclear Information System (INIS)

    Full text of publication follows: Ion sensitive probes [1, 2] serve to measure ion temperature in the SOL (Scrape-off layer) of tokamaks. The principle of the probe is based on geometrical shielding of the electrons coming from the plasma. Such a probe typically consists of a collector movable inside a metal shielding tube, which is oriented perpendicularly to the magnetic field. According to the standard theory, when the collector is retracted in the shielding tube, electrons with their small Larmor radii can not reach the collector surface. Thus, the probe becomes sensitive only to ions. However, the experimental results show a different feature, that the electron shielding is in general nonfunctional. It only works in the case, when the potential of the collector is same as the potential of the inside surface of the tube [3, 4]. This theory was a subject to verification in this paper. We have used full 3-Dimensional Particle-In-Cell cartesian code with fast multigrid Poisson solver. Using this code, we simulated the plasma behavior in the vicinity of a model of the probe. Potential structure at the entrance of the metal tube (tunnel) was identified. This structure produced E*B drifts which push electrons into the shielded space. A stream of electrons hitting the collector was observed for various potentials of the collector. Simulations revealed that electrons can penetrate even in strongly magnetized plasma (B = 1 T) inside the tube in all studied cases but when te the tube in all studied cases but when the potential of the collector is equal to the potential of the tube, they do not reach the collector. References: 1] I. Katsumata, Contributions to Plasma Physics 36S, (1996); 2] S.V. Ratynskaia Rev. Sci. Instrum., 73, (2002); 3] N. Ezumi, Contributions to Plasma Physics 41 (2001); 4] Adamek J. et al., Contributions to Plasma Physics 48 (2008). (authors)

  6. Equilibrium and non-equilibrium electron tunneling via discrete quantum states

    OpenAIRE

    Deshmukh, Mandar M.; Bonet, Edgar; Pasupathy, A N; Ralph, D.C.

    2001-01-01

    Tunneling is measured via the quantum levels of a metal nanoparticle. We analyze quantitatively the resonance energies, widths, and amplitudes, both in the regime where only one state is accessible for tunneling and in the non-equilibrium regime when additional states are made accessible one-by-one. For tunneling through one state, our results agree with expectations for sequential tunneling, but in the non-equilibrium regime the resonances are broadened and shifted in ways ...

  7. Building an electronic resource collection a practical guide

    CERN Document Server

    Lee, Stuart D

    2004-01-01

    This practical book guides information professionals step-by-step through building and managing an electronic resource collection. It outlines the range of electronic products currently available in abstracting and indexing, bibliographic, and other services and then describes how to effectively select, evaluate and purchase them.

  8. 2-dimensional hyperbolic medium for electrons and photons based on the array of tunnel-coupled graphene nanoribbons

    OpenAIRE

    Iorsh, Ivan; Trushkov, Iurii

    2015-01-01

    We study the electronic band structure and optical conductivity of an array of tunnel-coupled array of graphene nanoribbons. We show that due to the coupling of electronic edge states for the zigzag nanoribbon structure, the Fermi surface can become a hyperbola similarly to the case of the layered metal-dielectric structures, where the hyperbolic isofrequency contours originate from the coupling of localized surface plasmon polaritons. Moreover, we show that for both types o...

  9. Scanning tunneling microscopy investigations of hydrogen plasma-induced electron scattering centers on single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    The authors report on the generation of localized defects on single-walled carbon nanotubes by means of a hydrogen electron cyclotron resonance plasma. The defects have been investigated using scanning tunneling microscopy (STM) and show an apparent topographic height in the STM of 1-3 A. In the vicinity of defects, characteristic superstructures could be observed and the patterns could be simulated using a simple model based on large momentum scattering of the valence electrons. The combination of low structural damage and high electronic activity opens the possibility to tune the electronic transport properties using such defects

  10. Analysis of electron direct tunneling current through very-thin gate oxides in MOS capacitors with the parallel-perpendicular kinetic energy components and anisotropic masses

    Scientific Electronic Library Online (English)

    Fatimah Arofiati, Noor; Mikrajuddin, Abdullah; , Sukirno; , Khairurrijal.

    2010-12-01

    Full Text Available An electron direct tunneling current model of n+- poly - Si/SiO2/p - Si(100) metal-oxide-semiconductor (MOS) capacitors has been developed by considering a parallel-perpendicular kinetic energy coupling, which is represented by the gate electron phase velocity, and anisotropic masses under a parabol [...] ic E-k dispersion relationship. The electron effective mass in the oxide and the electron phase velocity in the n+ poly-Si gate are the only two fitting parameters to compare calculated tunneling currents to measured ones. It was obtained that the calculated tunneling currents fit well to the measured ones. The electron effective mass in the oxide layer tends to increase with decreasing the oxide thickness. In addition, the gate electron velocity is a constant of 1x10(5)m/s. Moreover, the theoretical model offers a simple treatment and an accurate result in obtaining the tunneling current.

  11. Electron-tunneling studies of thin films of high-T/sub c/ superconducting La-Sr-Cu-O

    International Nuclear Information System (INIS)

    We report results of the study of electron tunneling into thin films of the new high-T/sub c/ superconductor La-Sr-Cu-O. Both sandwich-type tunneling with a Pb counterelectrode and point-contact tunneling have been successfully achieved. The results show exceptionally large energy gaps in these materials (roughly 20, 30, and possibly even 60 mV), larger than previously obtained on bulk sintered powders. We interpret these results as due to large anisotropy in this material or due to the presence of a a very high-T/sub c/ layer near the surface of the films. The method of preparation of this new superconductor in thin film form is also discussed

  12. The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors

    CERN Document Server

    Scherer, H; Zorin, A B; Niemeyer, J C; Weimann, Th.

    2001-01-01

    The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors is reported. After treatment of the devices by annealing processes in forming gas atmosphere at different temperatures and for different times, distinct and reproducible changes of their resistance and capacitance values were found. According to the temperature regime, we observed different behaviors as regards the resistance changes, namely the tendency to decrease the resistance by annealing at T = 200 degree C, but to increase the resistance by annealing at T = 400 degree C. We attribute this behavior to changes in the aluminum oxide barriers of the tunnel junctions. The good reproducibility of these effects with respect to the changes observed allows the proper annealing treatment to be used for post-process tuning of tunnel junction parameters. Also, the influence of the annealing treatment on the noise properties of the transistors at low frequency was investigated. In no case did the noise figures in t...

  13. Non-perturbation theory of electronic dynamic conductivity for two-barrier resonance tunnel nano-structure

    Directory of Open Access Journals (Sweden)

    O.M. Voitsekhivska

    2011-12-01

    Full Text Available The non-perturbation theory of electronic dynamic conductivity for open two-barrier resonance tunnel structure is established for the first time within the model of rectangular potentials and different effective masses of electrons in the elements of nano-structure and the wave function linear over the intensity of electromagnetic field. It is proven that the results of the theory of dynamic conductivity, developed earlier in weak signal approximation within the perturbation method, qualitatively and quantitatively correlate with the obtained results. The advantage of non-perturbation theory is that it can be extended to the case of electronic currents interacting with strong electromagnetic fields in open multi-shell resonance tunnel nano-structures, as active elements of quantum cascade lasers and detectors.

  14. Quantum Tunneling Effects in the Ssh Model of Electron-Phonon Interactions

    Science.gov (United States)

    Quémerais, Pascal; Campbell, David K.; Raimbault, Jean-Luc; Aubry, Serge

    We examine the Su-Schrieffer-Heeger (SSH) model of electron-phonon (e-p) interactions as an example of a theory in which commensurate and incommensurate bond-order wave (BOW) ground states are generated (in the quasi-one-dimensional (quasi 1-D) case) by an intersite e-p coupling. We focus primarily on the two-fold commensurate situation, in view of its applicability to the important quasi 1-D conducting polymer trans-polyacetylene (trans — (CH)x). Using a coherent state formalism to model the quantum fluctuation corrections to the adiabatic ground state, we study the quantum tunneling of the SSH “solitons” (viewed as discommensurations created in the two-fold commensurate ground state) and show that, as a result of this tunneling, the energy of the discommensurations can become negative for e-p couplings below a certain critical coupling. We argue that this negative defect energy is an indication of the instability of the underlying adiabatic commensurate BOW state. The critical e-p coupling for this transition depends on the phonon frequency and, for general commensurability, on the commensurability ratio. Thus, in real trans — (CH)x chains where the e-p coupling and the bare phonon frequency are fixed, the transition we describe can occur as a function of doping (which can change the effective commensurability) and may explain the BOW-to-quasimetal transition in doped (CH)x. For quasi-1-D systems, we also estimate the critical e-p couplings for the three-fold commensurate and incommensurate cases. We conclude by mentioning possible extensions of our approach and results to the new family of “fullerenes”, Cn(n?60).

  15. Grain boundary tunnel spectroscopy of the electron-doped cuprate superconductor La2-xCexCuO4

    International Nuclear Information System (INIS)

    The electron doped superconductor La2-xCexCuO4 (LCCO) has been investigated by electric transport measurements at low temperatures T down to 5 K and high magnetic fields up to 16 T. For this purpose LCCO thin film tunnel junctions have been prepared on bicrystal substrates by molecular beam epitaxy and micro structuring. The samples were characterised by measuring the thin film resistivity and the tunnel conductance of quasi particles across the grain boundary. By these measurements an unconventional symmetry of the order parameter could be revealed for La2-xCexCuO4. Furthermore it was shown, that the tunnel conductance can be used as a probe for the upper critical field Bc2(T). By using this method a value of Bc2?24 T has been found for La2-xCexCuO4, a value roughly three times bigger than previously known. By this observation it was shown that the superconducting phase covers a larger region in the B-T-phase diagram. In addition it was concluded, that the pseudogap phase in La2-xCexCuO4 is either not existent at all or covers only a small temperature region. Besides quasiparticle tunneling also the tunneling of Cooper pairs in small magnetic fields has been investigated. It was shown that the critical current across the grain boundary depends on the supplier of the bicrystal substrate. (orig.)

  16. Predicting the Rate Constant of Electron Tunneling Reactions at the CdSe-TiO2 Interface.

    Science.gov (United States)

    Hines, Douglas A; Forrest, Ryan P; Corcelli, Steven A; Kamat, Prashant V

    2015-06-18

    Current interest in quantum dot solar cells (QDSCs) motivates an understanding of the electron transfer dynamics at the quantum dot (QD)-metal oxide (MO) interface. Employing transient absorption spectroscopy, we have monitored the electron transfer rate (ket) at this interface as a function of the bridge molecules that link QDs to TiO2. Using mercaptoacetic acid, 3-mercaptopropionic acid, 8-mercaptooctanoic acid, and 16-mercaptohexadecanoic acid, we observe an exponential attenuation of ket with increasing linker length, and attribute this to the tunneling of the electron through the insulating linker molecule. We model the electron transfer reaction using both rectangular and trapezoidal barrier models that have been discussed in the literature. The one-electron reduction potential (equivalent to the lowest unoccupied molecular orbital) of each molecule as determined by cyclic voltammetry (CV) was used to estimate the effective barrier height presented by each ligand at the CdSe-TiO2 interface. The electron transfer rate (ket) calculated for each CdSe-ligand-TiO2 interface using both models showed the results in agreement with the experimentally determined trend. This demonstrates that electron transfer between CdSe and TiO2 can be viewed as electron tunneling through a layer of linking molecules and provides a useful method for predicting electron transfer rate constants. PMID:25532024

  17. The impact of subject-specific electronic resources on the research process using ERIC (Education Resources Information Center) and SciFinder Scholar electronic resources as exemplars.

    OpenAIRE

    Love-Rodgers, Christine; Stewart, Rowena

    2006-01-01

    As part of a UK wide study attempting to assess the impact libraries have on the work and study of their members, Edinburgh University Library (EUL) decided to “measure the impact of subject-specific electronic resources on the research process”, using the ERIC (Education Resources Information Center) and SciFinder Scholar electronic resources as exemplars. The project methodology included analysis of the databases’ coverage of University of Edinburgh research publications and surv...

  18. Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin

    2009-01-01

    We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.

  19. Developing an Electronic Resource Management System: Verde from Ex Libris

    Directory of Open Access Journals (Sweden)

    Tamar Sadeh

    2004-10-01

    Full Text Available Rapid growth in the number of electronic resources and the complexity of managing e-collections has posed new challenges for libraries and hence requires the development of new tools. To meet this need, Ex Libris is developing a new product, an electronic resource management (ERM system. The development process began in 2002 and has benefited from the company's 25 years of experience in providing libraries with various products - an integrated library system, digital asset management system, library portal, and link server. Working with an international focus group and development partners and interacting with the Digital Library Federation's Electronic Resource Management Initiative (DLF ERMI committee, Ex Libris explored the various aspects of the e-resource life cycle. As a result, the Ex Libris ERM system was designed to address the issues raised through this collaboration and the DLF requirements. The interface of the system represents all of its components; it includes navigation options and facilitates workflows that support the various activities that librarians perform when dealing with electronic resources. This paper describes the development process of the Ex Libris ERM system. The emphasis is on the particular functionality required for managing e-resources and the ways in which existing systems in the library arena can handle specific tasks.

  20. Single-electron charging effects and implications for tunneling measurements of the high-T/sub c/ superconductors

    International Nuclear Information System (INIS)

    The authors present a theory for the dynamics of two voltage-biased, ultra-small-capacitance tunnel junctions connected in series when one or more electrodes are superconducting and experiments performed on parallel arrays of such junctions. Using the semiclassical model, they find that the I-V characteristics display steps and therefore multiple peaks in dI/dV, corresponding to the time-average occupation of the interjunction region by integral numbers of electrons. The voltage at which the first step is located depends on the superconducting gap, ?(T), and the capacitances of the junctions. The spacing between subsequent steps depends solely on the capacitances. They discuss electron tunneling results performed on metal/Al/sub 2/O/sub 3//2-10 nm-diameter metal particles/Al/sub 2/O/sub 3//metal junctions where this multiple-peak structure is observed. They present preliminary tunneling results in junctions employing Pb-particles, where they observe a shift of the peaks when the sample is cooled below T/sub c/ of Pb consistent with theory. Taken together, these results indicate that the multiple-peak structure commonly observed in tunneling data of high-T/sub c/ oxide superconductors can be explained in terms of charging effects in a material with a single superconducting gap. Finally, they discuss possible applications in a new type of transistor element

  1. Titanium Silicide Islands on Atomically Clean Si(100): Identifying Single Electron Tunneling Effects

    OpenAIRE

    Tedesco, Joseph L.; Rowe, J. E.; Nemanich, Robert J.

    2010-01-01

    Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (< 2 nm) on atomically clean Si(100) substrates followed by annealing to ~800 degrees C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to...

  2. Why and How to Measure the Use of Electronic Resources

    Directory of Open Access Journals (Sweden)

    Jean Bernon

    2008-11-01

    Full Text Available A complete overview of library activity implies a complete and reliable measurement of the use of both electronic resources and printed materials. This measurement is based on three sets of definitions: document types, use types and user types. There is a common model of definitions for printed materials, but a lot of questions and technical issues remain for electronic resources. In 2006 a French national working group studied these questions. It relied on the COUNTER standard, but found it insufficient and pointed out the need for local tools such as web markers and deep analysis of proxy logs. Within the French national consortium COUPERIN, a new working group is testing ERMS, SUSHI standards, Shibboleth authentication, along with COUNTER standards, to improve the counting of the electronic resources use. At this stage this counting is insufficient and its improvement will be a European challenge for the future.

  3. The Study of Analytical Model of Library Electronic Resources Usage-A Case of Medical Electronic Resources

    Directory of Open Access Journals (Sweden)

    Chung-Yen Yu

    2014-10-01

    Full Text Available With the advents of internet, the importance of electronic resources is growing. Due to the increasing expensiveness of electronic resources, university libraries normally received budgets from parent institutions annually. They necessarily applied effective and systematic methods for decision making in electronic resources purchase or re-subscription. However, there are some difficulties in practices: First of all, libraries are unable to receive user records; second, the COUNTER statistics does not include details about users and their affiliation. As a result, one cannot conduct advanced user analysis based on the usage of users, institutions, and departments. To overcome the difficulties, this study presents a feasible model to analyze electronic resource usage effectively and flexibly. We set up a proxy server to collect actual usage raw data. By analyzing items in internet browsing records, associated with original library automatic system, this study aims at exploring how to use effective ways to analyze big data of website log data. We also propose the process of how original data to be transformed, cleared, integrated, and demonstrated. This study adopted a medical university library and its subscription of medical electronic resources as a case. Our data analysis includes (1 year of subscription,(2 title of journal, (3 affiliation, (4 subjects, and (5 specific journal requirements, etc. The findings of the study are contributed to obtain further understanding in policy making and user behavior analysis. The integrated data provides multiple applications in informatics research, information behavior, bibliomining, presenting diverse views and extended issues for further discussion.

  4. Electronic Resources Security: A look at Unauthorized Users

    OpenAIRE

    Heather Tones White

    2010-01-01

    Much of the literature written on electronic resources security focuses on systematic downloading.  However, when the unauthorized use from two cases of stolen identities at the University of Saskatchewan was studied in more depth, a different pattern emerged.  By analyzing proxy server data, we found that the unauthorized use was coming from all over the world, was focused on science, technology and medical resources, and included both small-scale and excessive downloading.  This article ...

  5. Access to electronic resources by visually impaired people

    Directory of Open Access Journals (Sweden)

    Jenny Craven

    2003-01-01

    Full Text Available Research into access to electronic resources by visually impaired people undertaken by the Centre for Research in Library and Information Management has not only explored the accessibility of websites and levels of awareness in providing websites that adhere to design for all principles, but has sought to enhance understanding of information seeking behaviour of blind and visually impaired people when using digital resources.

  6. 2-dimensional hyperbolic medium for electrons and photons based on the array of tunnel-coupled graphene nanoribbons

    CERN Document Server

    Iorsh, Ivan

    2015-01-01

    We study the electronic band structure and optical conductivity of an array of tunnel-coupled array of graphene nanoribbons. We show that due to the coupling of electronic edge states for the zigzag nanoribbon structure, the Fermi surface can become a hyperbola similarly to the case of the layered metal-dielectric structures, where the hyperbolic isofrequency contours originate from the coupling of localized surface plasmon polaritons. Moreover, we show that for both types of the ribbon edge, the optical response of the structure can be characterized by a uniaxial conductivity tensor, having principal components of the different signs. Therefore, the tunnel-coupled nanoribbon array can be regarded as a tunable hyperbolic metasurface.

  7. Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

    Science.gov (United States)

    Yang, Zhichao; Zhang, Yuewei; Nath, Digbijoy N.; Khurgin, Jacob B.; Rajan, Siddharth

    2015-01-01

    We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm2. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

  8. Design and simulation of a novel GaN based resonant tunneling high electron mobility transistor on a silicon substrate

    Science.gov (United States)

    Chowdhury, Subhra; Chattaraj, Swarnabha; Biswas, Dhrubes

    2015-04-01

    For the first time, we have introduced a novel GaN based resonant tunneling high electron mobility transistor (RTHEMT) on a silicon substrate. A monolithically integrated GaN based inverted high electron mobility transistor (HEMT) and a resonant tunneling diode (RTD) are designed and simulated using the ATLAS simulator and MATLAB in this study. The 10% Al composition in the barrier layer of the GaN based RTD structure provides a peak-to-valley current ratio of 2.66 which controls the GaN based HEMT performance. Thus the results indicate an improvement in the current–voltage characteristics of the RTHEMT by controlling the gate voltage in this structure. The introduction of silicon as a substrate is a unique step taken by us for this type of RTHEMT structure.

  9. The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors

    OpenAIRE

    Scherer, H.; Weimann, Th.; A. B. Zorin; Niemeyer, J

    2001-01-01

    The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors is reported. After treatment of the devices by annealing processes in forming gas atmosphere at different temperatures and for different times, distinct and reproducible changes of their resistance and capacitance values were found. According to the temperature regime, we observed different behaviors as regards the resistance changes, namely the tendency to decrease the resi...

  10. Relativistic calculation of the electron-momentum shift in tunneling ionization

    Science.gov (United States)

    Ivanov, I. A.

    2015-04-01

    We describe a procedure for the solution of the time-dependent Dirac equation. The procedure is based on the relativistic generalization of the matrix iteration method. We use this procedure to study electron-momentum distribution along the laser-beam propagation direction for the process of the tunneling ionization of a hydrogen atom. We found, in agreement with the experimental observations [C. T. L. Smeenk, L. Arissian, B. Zhou, A. Mysyrowicz, D. M. Villeneuve, A. Staudte, and P. B. Corkum, Phys. Rev. Lett. 106, 193002 (2011), 10.1103/PhysRevLett.106.193002], that relativistic effects lead to appreciable deviation of the distribution from the strict left-right symmetry present in the nonrelativistic case. The expectation value of the momentum along the laser-beam propagation direction grows linearly with intensity and follows closely the behavior of the expectation value of the kinetic energy divided by the speed of light. These features agree with the experimental results [C. T. L. Smeenk, L. Arissian, B. Zhou, A. Mysyrowicz, D. M. Villeneuve, A. Staudte, and P. B. Corkum, Phys. Rev. Lett. 106, 193002 (2011), 10.1103/PhysRevLett.106.193002].

  11. Room-temperature single-electron tunnelling in surfactant stabilised iron oxide nanoparticles

    Science.gov (United States)

    Moore, R. G. C.; Evans, S. D.; Shen, T.; Hodson, C. E. C.

    2001-02-01

    Iron oxide nanoparticles have been synthesised by the reduction of FeCl 3·6H 2O and FeCl 2·4H 2O (mass ratio 2:1) in propan-2-ol. The particles were stabilised by the addition of lauric acid and the resultant particles could be readily dispersed in chloroform. Room-temperature single-electron tunnelling through these iron oxide particles has been achieved (to our knowledge) for the first time, using an STM tip-particle-substrate double junction. Characterisation of the particles by XPS and FTIR show that they are Fe 2O 3, or possibly Fe 3O 4 with an outer layer of Fe 2O 3, coated with a carboxylic acid monolayer. The particle diameter given by TEM is of the order of 5.0±0.9 nm. From the Coulomb staircase behaviour observed in the I- V curves, we estimate a nanoparticle capacitance of 6.7×10 -19 F which is in agreement with that expected for particles of this size.

  12. Combining scanning tunneling microscopy and synchrotron radiation for high-resolution imaging and spectroscopy with chemical, electronic, and magnetic contrast

    International Nuclear Information System (INIS)

    The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM. -- Highlights: ? Synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system designed. ? Unique STM mount design allows angular DOF for tip alignment with x-ray beam. ? System demonstrates ability to resolve atomic corrugations on HOPG. ? Studies show chemical sensitivity with STM tip from photocurrent and tunneling. ? Results show system's ability to study local magnetic (XMCD) properties on Fe films.

  13. Scanning tunneling microscopy study of the electron transport properties of self-assembled monolayers of bis-phenyloxazoles

    Science.gov (United States)

    Park, Hayn; Lee, Whasil; Klare, Jennifer E.; Nuckolls, Colin; Heinz, Tony F.

    2004-03-01

    The self-assembly and electron transport properties of monothiol-terminated bis-phenyloxazole molecules have been studied by scanning tunneling microscopy and spectroscopy. The molecules were deposited on a clean Au(111) surface from solution and were studied under vacuum. In the as-deposited state, no long-range ordering was present. Upon annealing, however, an ordered monolayer was observed, characterized by well-defined columnar structures. The height of the corrugations was compatible with molecules aligned normal to the surface. This structure is attributed to the orthogonal terphenyl arms in the cruciform species study, which act to inhibit the molecules from assuming a prone position.[1] Scanning tunneling spectroscopy revealed a relatively high conductance, as expected for the conjugated electron system. Threshold features in the I-V characteristics were observed, indicative of resonant tunneling processes. The electronic properties of the molecules will be discussed in the context of the HOMO-LUMO gap deduced from complementary optical absorption data. [1] J. E. Klare et al., JACS 125, 6030 (2003).

  14. Characterization and Properties of Oligothiophenes Using Scanning Tunneling Microscopy for Possible Use in Organic Electronics

    International Nuclear Information System (INIS)

    A scanning tunneling microscopy study has been made on a group of alkyl-substituted oligothiophenes. The self-assembled monolayers of this type of semi-conducting oligomers on graphite were observed and characterized. To control the self-assembly, it is important to first understand the forces that drive the spontaneous ordering of molecules at interfaces. For the identification of the forces, several substituted oligothiophenes were examined: carboxylic acid groups, methyl ester carboxylic acid, and iodine atoms at one end and benzyl esters at the other end of the oligomers this is in addition to the non-functionalized oligothiophehens, Self-assembled monolayers of these molecules were then examined by STM. A detailed analysis of the driving forces and parameters controlling the formation of the self-assembled 2- D crystal monolayers was carried out by performing modeling of the experimental observations. The theoretical calculations gave us a conclusive insight into the intermolecular interactions, which lead to the observed conformation of molecules on the surface. An attempt to react two iodinated oligomers on the surface after the formation of the monolayer has been done; a topochemical reaction studies using UV/Vis light irradiation has been preceded. The targeted reaction was achieved. This can be considered as a great step towards the formation of nano-wires and other organic electronic devices. The applicability of the above method of force-driven self organisation in different patterns was examined as template for building donor-nano structures for electronic devices. It was necessary to examine the stability of the formed templates in air. The monolayers were left to dry and STM images were taken; C60 was then added to the monolayer, and the complexation of the C60 (as acceptor) with the formed monolayer template was examined.

  15. Electronic Commerce Resource Centers. An Industry--University Partnership.

    Science.gov (United States)

    Gulledge, Thomas R.; Sommer, Rainer; Tarimcilar, M. Murat

    1999-01-01

    Electronic Commerce Resource Centers focus on transferring emerging technologies to small businesses through university/industry partnerships. Successful implementation hinges on a strategic operating plan, creation of measurable value for customers, investment in customer-targeted training, and measurement of performance outputs. (SK)

  16. Providing Access to Electronic Information Resources in Further Education

    Science.gov (United States)

    Banwell, Linda; Ray, Kathryn; Coulson, Graham; Urquhart, Christine; Lonsdale, Ray; Armstrong, Chris; Thomas, Rhian; Spink, Sin; Yeoman, Alison; Fenton, Roger; Rowley, Jennifer

    2004-01-01

    This article aims to provide a baseline for future studies on the provision and support for the use of digital or electronic information services (EIS) in further education. The analysis presented is based on a multi-level model of access, which encompasses access to and availability of information and communication technology (ICT) resources

  17. What Is the Future of Electronic Resource Management Systems?

    Science.gov (United States)

    Tijerina, Bonnie; King, Douglas

    2008-01-01

    In a time of constant change, sometimes it is worthwhile to ruminate on the future and how things ought to be. "Journal of Electronic Resources Librarianship" wanted to capture some of these ruminations from around the field in a new column called "E-Opinions from the Field" where readers are asked to send in their thoughts on a topic and respond…

  18. Think Locally: A Prudent Approach to Electronic Resource Management Systems

    Science.gov (United States)

    Gustafson-Sundell, Nat

    2011-01-01

    A few articles have drawn some amount of attention specifically to the local causes of the success or failure of electronic resource management system (ERMS) implementations. In fact, it seems clear that local conditions will largely determine whether any given ERMS implementation will succeed or fail. This statement might seem obvious, but the…

  19. Optical switching of single-electron tunneling in SiO2/molecule/SiO2 multilayer on Si(100)

    International Nuclear Information System (INIS)

    Porphyrin-based molecules inserted into the oxide layer of a metal-oxide-semiconductor structure served as Coulomb islands. A Coulomb staircase originating from the single-electron tunneling was observed in a current-voltage curve. We found that light irradiation induced a shift in the Coulomb staircase. This shift was reversible; the shifted Coulomb staircase returned to its original position when the light irradiation was turned off. We thus demonstrated optical switching of a tunneling current. This result indicates that the molecular Coulomb islands have the potential to provide a range of optical functionality in single-electron tunneling devices

  20. The Electronic Clearinghouse for Exemplary Engineering Technology Resources

    Science.gov (United States)

    The Electronic Clearinghouse for Exemplary Engineering Technology Resources (or NETEC) is a site created with substantial funding from the National Science Foundation. Drawing on the teaching experiences and resources developed by many concerned persons in industry and academic settings, the Clearinghouse contains everything from course materials for material engineering to journal articles that deal with the science (and art) of teaching in the subfields of engineering. First-time visitors may wish to register on the homepage, and then proceed to browse through the â??Clearinghouse Resourcesâ? area. Here they can click on an alphabetized list of terms, such as digital electronics and skill standards, and look through the available materials. Of course, there is a great deal more available here than the very fine educational resources, as visitors can also look over online job boards and mentorship opportunities.

  1. Electronic Transport in Single Molecule Junctions: Control of the Molecule-Electrode Coupling Through Intramolecular Tunneling Barriers

    DEFF Research Database (Denmark)

    Danilov, Andrey; Kubatkin, Sergey

    2008-01-01

    We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes. One derivative has additional methylene groups separating the thiols from the delocalized -electron system. The insertion of methylene groups changes the open state conductance by 3-4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.

  2. Conceptual design of a 100 MW electron beam accelerator module for the National Hypersonic Wind Tunnel Program

    International Nuclear Information System (INIS)

    The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1-2 MeV at a total average beam power of 100-200 MW for several seconds. Although a 100 MW module is a two-order extrapolation from demonstrated average power levels, the scaling of accelerator components appears reasonable. This paper will present an evaluation of component and system issues involved in the design of a 100 MW electron beam accelerator module with precision beam transport into a high pressure flowing air environment

  3. Impact of phonon-assisted tunneling on electronic conductivity in graphene nanoribbons and oxides ones

    Directory of Open Access Journals (Sweden)

    Antanas Kiveris

    2010-10-01

    Full Text Available Phonon-assisted tunneling (PhAT model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed model describes well not only current dependence on temperature but also the temperature-dependent I-V data using the same set of parameters characterizing material under investigation. The values of active phonons energy and field strength for tunneling are estimated from the fit of current dependence on temperature and I-V/T data with the phonon-assisted tunneling theory.

  4. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors

    International Nuclear Information System (INIS)

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of Hc2(T) respectively Hc2(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown

  5. ASIL Guide to Electronic Resources for International Law

    Science.gov (United States)

    Hoffman, Marci.

    2003-01-01

    The study and practice of international law can be a tough area to get a handle on, and with numerous online resources available for both areas, it can be difficult to separate the wheat from the chaff. Since 1997, The American Society of International Law (ASIL) has been continuously updating and revising their Guide to Electronic Resources for International Law, under the able direction of Marci Hoffman and Jill Watson. Within each of its eight primary sections, users can read about various high-quality online resources for each topical area (such as international organizations and human rights), and then read brief summaries of what each online resource features in terms of its content and scope. As might be expected, the site also contains information on relevant and helpful weblogs that deal with international law.

  6. Tunneling: From Milliseconds to Attoaseconds

    OpenAIRE

    Nimtz, Guenter

    2009-01-01

    How much time does a wave packet spent in tunneling a barrier? Quantum mechanical calculations result in zero time inside a barrier. In the nineties analogous tunneling experiments with microwaves were carried out confirming quantum mechanics. Electron tunneling time is hard to measure being extremely short. However, quite recently the atomic ionization tunneling time has been measured. Experimental data of photonic, phononic, and electronic tunneling time is available now. ...

  7. Asymmetric tunneling rates for electrons and holes at CdSe quantum dot/carbon nanotube interfaces

    Science.gov (United States)

    Ismail-Beigi, Sohrab; Jiang, Jie

    2014-03-01

    Decorating carbon nanotubes with CdSe quantum dots (QDs) is one potential approach for creating high efficiency photovoltaics. Our collaborators at Yale recently produced a ligand-free covalent attachment of CdSe QDs to carbon nanotubes through an organic ligand exchange mechanism. Our prior first principles work described the energetics of the various binding processes and rationalized the experimental growth methodology. After a brief review of the system, we will describe our intriguing finding that excited electrons and holes tunnel with different rates out of the QD and into the carbon nanotubes. The asymmetric tunneling rate itself can, in principle, boost the separation of photo-excited charge at the interface even if there are insufficient band energy differences across the interface. We describe our results for the tunneling rates computed using (i) a brute force approach with increasing simulation cell size to remove periodic effects, and (ii) a Green's function method that directly connects the QD to a thermodynamically large electron reservoir (e.g., a very long pristine nanotube). Supported by NSF SOLAR DMR 0934520.

  8. Exploring the Tilt-Angle Dependence of electron tunneling across Molecular junction of Self-Assembled Alkanethiols

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.

    2009-01-01

    Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current?voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect.

  9. Electronic characterization of LaAlO3-SrTiO3 interfaces by scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    When LaAlO3 is epitaxially grown on TiO2-terminated SrTiO3, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO3 and SrTiO3, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO3-SrTiO3 interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  10. E-Resources Management: How We Positioned Our Organization to Implement an Electronic Resources Management System

    Science.gov (United States)

    White, Marilyn; Sanders, Susan

    2009-01-01

    The Information Services Division (ISD) of the National Institute of Standards and Technology (NIST) positioned itself to successfully implement an electronic resources management system. This article highlights the ISD's unique ability to "team" across the organization to realize a common goal, develop leadership qualities in support of…

  11. Negative refractive index electron `optics', pseudospintronics and chiral tunneling in graphene pn junction -- beating the Landauer switching limit?

    Science.gov (United States)

    Sajjad, Redwan; Pan, Chenyun; Naeemi, Azad; Ghosh, Avik

    2013-03-01

    We use atomistic quantum kinetic calculations to demonstrate how graphene PN junctions can switch with high ON currents, low OFF currents, steep gate transfer characteristics and unipolar rectification. The physics of such unconventional switching relies on (a) field-engineering with patterned gates to create a transmission gap, by sequential filtering of all propagating modes, and (b) using tilted junctions to suppress Klein tunneling under appropriate gate biasing, making that transmission gap gate tunable. The doping ratio of the junction dictates the energy range over which the tilt angle exceeds the critical angle for transmission, generating thereby a gate tunable transmission gap that enables switching at voltages less than the Landauer-Shannon thermal limit. The underlying physics involves a combination of `electron optics' driven by Snell's law, negative index metamaterial with a PN junction, and pseudospin driven chiral tunneling, for which we also present experimental verification. [Sajjad et al, APL 99, 123101 (2011); Sajjad et al, PRB 86, 155412 (2012)]. We use atomistic quantum kinetic calculations to demonstrate how graphene PN junctions can switch with high ON currents, low OFF currents, steep gate transfer characteristics and unipolar rectification. The physics of such unconventional switching relies on (a) field-engineering with patterned gates to create a transmission gap, by sequential filtering of all propagating modes, and (b) using tilted junctions to suppress Klein tunneling under appropriate gate biasing, making that transmission gap gate tunable. The doping ratio of the junction dictates the energy range over which the tilt angle exceeds the critical angle for transmission, generating thereby a gate tunable transmission gap that enables switching at voltages less than the Landauer-Shannon thermal limit. The underlying physics involves a combination of `electron optics' driven by Snell's law, negative index metamaterial with a PN junction, and pseudospin driven chiral tunneling, for which we also present experimental verification. [Sajjad et al, APL 99, 123101 (2011); Sajjad et al, PRB 86, 155412 (2012)]. Authors acknowledge financial grant from NRI-INDEX

  12. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires

    International Nuclear Information System (INIS)

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement with a gate has provided the resistance of the nanowire. From the dimensions of the nanowire the resistivity was calculated. The obtained resistivity was found to be in agreement with literature values. In addition, the contact resistances of the tunneling tips on the silicide nanowires were determined.

  13. Electronic Resources and Mission Creep: Reorganizing the Library for the Twenty-First Century

    Science.gov (United States)

    Stachokas, George

    2009-01-01

    The position of electronic resources librarian was created to serve as a specialist in the negotiation of license agreements for electronic resources, but mission creep has added more functions to the routine work of electronic resources such as cataloging, gathering information for collection development, and technical support. As electronic…

  14. Electronic properties of conductive pili of the metal-reducing bacterium Geobacter sulfurreducens probed by scanning tunneling microscopy

    Science.gov (United States)

    Veazey, Joshua P.; Reguera, Gemma; Tessmer, Stuart H.

    2011-12-01

    The metal-reducing bacterium Geobacter sulfurreducens produces conductive protein appendages known as “pilus nanowires” to transfer electrons to metal oxides and to other cells. These processes can be harnessed for the bioremediation of toxic metals and the generation of electricity in bioelectrochemical cells. Key to these applications is a detailed understanding of how these nanostructures conduct electrons. However, to the best of our knowledge, their mechanism of electron transport is not known. We used the capability of scanning tunneling microscopy (STM) to probe conductive materials with higher spatial resolution than other scanning probe methods to gain insights into the transversal electronic behavior of native, cell-anchored pili. Despite the presence of insulating cellular components, the STM topography resolved electronic molecular substructures with periodicities similar to those reported for the pilus shaft. STM spectroscopy revealed electronic states near the Fermi level, consistent with a conducting material, but did not reveal electronic states expected for cytochromes. Furthermore, the transversal conductance was asymmetric, as previously reported for assemblies of helical peptides. Our results thus indicate that the Geobacter pilus shaft has an intrinsic electronic structure that could play a role in charge transport.

  15. On the valve nature of a monolayer of aligned molecular magnets in tunneling spin-polarized electrons: Towards organic molecular spintronics

    Energy Technology Data Exchange (ETDEWEB)

    Chakrabarti, Sudipto; Pal, Amlan J., E-mail: sspajp@iacs.res.in [Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2014-01-06

    We form a monolayer of magnetic organic molecules and immobilize their moments pointing either upwards or downwards with respect to the substrate through an electrostatic-binding process. Such a monolayer is probed with a scanning tunneling microscope tip, which is also magnetized with the magnetization vector pointing towards (or away from) apex of the tip. From spin-polarized tunneling current, we show that the current was higher when magnetization vectors of the tip and molecules were parallel as compared to that when they were anti-parallel. We show that for tunneling of spin-polarized electrons, aligned organic molecular magnets can act as a valve.

  16. On the valve nature of a monolayer of aligned molecular magnets in tunneling spin-polarized electrons: Towards organic molecular spintronics

    International Nuclear Information System (INIS)

    We form a monolayer of magnetic organic molecules and immobilize their moments pointing either upwards or downwards with respect to the substrate through an electrostatic-binding process. Such a monolayer is probed with a scanning tunneling microscope tip, which is also magnetized with the magnetization vector pointing towards (or away from) apex of the tip. From spin-polarized tunneling current, we show that the current was higher when magnetization vectors of the tip and molecules were parallel as compared to that when they were anti-parallel. We show that for tunneling of spin-polarized electrons, aligned organic molecular magnets can act as a valve

  17. Revealing energy level structure of individual quantum dots by tunneling rate measured by single-electron sensitive electrostatic force spectroscopy.

    Science.gov (United States)

    Roy-Gobeil, Antoine; Miyahara, Yoichi; Grutter, Peter

    2015-04-01

    We present theoretical and experimental studies of the effect of the density of states of a quantum dot (QD) on the rate of single-electron tunneling that can be directly measured by electrostatic force microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic force microscope cantilever tip modulates the charge state of a QD in the Coulomb blockade regime. The charge dynamics of the dot, which is detected through its back-action on the capacitavely coupled cantilever, depends on the tunneling rate of the QD to a back-electrode. The density of states of the QD can therefore be measured through its effect on the energy dependence of tunneling rate. We present experimental data on individual 5 nm colloidal gold nanoparticles that exhibit a near continuous density of state at 77 K. In contrast, our analysis of already published data on self-assembled InAs QDs at 4 K clearly reveals discrete degenerate energy levels. PMID:25761141

  18. Single-shot read-out of electron spin states in a quantum dot using spin-dependent tunnel rates

    CERN Document Server

    Hanson, R; Vink, I T; Elzerman, J M; Naber, W J M; Koppens, F H L; Kouwenhoven, L P; Vandersypen, L M K

    2005-01-01

    We present a method for reading out the spin state of electrons in a quantum dot that is robust against charge noise and can still be used when the electron temperature exceeds the energy splitting between the states. A spin dependence of the tunnel rates is used to correlate the spin states to different charge states. A subsequent fast measurement of the charge on the dot then reveals the original spin state. We experimentally demonstrate the method by performing read-out of the two-electron spin states, achieving a single-shot visibility of more than 80%. We find very long triplet-to-singlet relaxation times (up to several milliseconds), with an in-plane magnetic field dependence consistent with spin-orbit coupling as the dominant source of relaxation.

  19. Electron-tunneling studies on CeCoIn5 heavy-fermion thin films and microstructures

    International Nuclear Information System (INIS)

    In many cases, the availability of high-quality thin films of a material under study allows to gain valuable physical insight into its properties. For example, when thin films are available, planar tunneling spectroscopy or quantum mechanical interferometry techniques can be used to probe the electronic properties in a very direct way. In this work, we study the rich but poorly understood electronic properties of the heavy-fermion compound CeCoIn5. Numerous attempts to grow homogeneous CeCoIn5 thin films of the desired quality have not been successful. Our work therefore pursuits two goals: (1) to improve the CeCoIn5 thin film quality using the molecular beam epitaxy and (2) to investigate the low-temperature electronic properties of the CeCoIn5 thin films using direct probing methods.

  20. Conceptual Design of a 50-100 MW Electron Beam Accelerator System for the National Hypersonic Wind Tunnel Program

    International Nuclear Information System (INIS)

    The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1--2 MeV at a beam power level of 50--100 MW. Direct-current electron accelerator technology can readily generate high average power beams to approximately 5 MeV at output efficiencies greater than 90%. However, due to the nature of research and industrial applications, there has never been a requirement for a single module with an output power exceeding approximately 500 kW. Although a 50--100 MW module is a two-order extrapolation from demonstrated power levels, the scaling of accelerator components appears reasonable. This paper presents an evaluation of component and system issues involved in the design of a 50--100 MW electron beam accelerator system with precision beam transport into a high pressure flowing air environment

  1. A hydrogen-bonded electron-tunneling circuit reads the base composition of unmodified DNA

    International Nuclear Information System (INIS)

    Using a tunnel junction in which one electrode is guanidinium-functionalized (to trap DNA via hydrogen bonding to the backbone phosphates) and a second electrode which is functionalized with a base (to capture its complementary target on the DNA), current versus distance curves are obtained which yield an accurate measure of the base composition of DNA oligomers. With this long tunneling path, resolution is limited to sequence blocks of about twenty bases or larger, because of the need to form a large-area tunnel junction. A shorter hydrogen-bonded path across bases will be required for DNA sequencing. Nonetheless, these measurements point the way to a new type of nanoscale sensor.

  2. Quasi-stationary states of electrons interacting with strong electromagnetic field in two-barrier resonance tunnel nano-structure

    Directory of Open Access Journals (Sweden)

    M.V. Tkach

    2012-10-01

    Full Text Available An exact solution of non-stationary Schrodinger equation is obtained for a one-dimensional movement of electrons in an electromagnetic field with arbitrary intensity and frequency. Using it, the permeability coefficient is calculated for a two-barrier resonance tunnel nano-structure placed into a high-frequency electromagnetic field. It is shown that a nano-structure contains quasi-stationary states the spectrum of which consists of the main and satellite energies. The properties of resonance and non-resonance channels of permeability are displayed.

  3. Electron tunneling measurements in LaSrCuO and YBaCuO

    International Nuclear Information System (INIS)

    The authors analyze the break junction technique, whereby vacuum tunneling occurs within the fracture of a bulk sample to study the LaSrCuO and YBaCuO perovskite superconductors. Structure in the current-versus-voltage characteristics is reminiscent of previous quasiparticle curves obtained for BCS superconducting materials. Some curves have anomalous qualities, including large dips in the junction conductance with increasing voltage just above a well defined tunneling gap edge, linearly increasing junction conductance with applied bias, features occurring near 1, 3, 5 voltage intervals

  4. Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling

    CERN Document Server

    Hassel, J; Seppä, H; Hakonen, P J

    2003-01-01

    We study a circuit where a mesoscopic Josephson junction (JJ) is embedded in an environment consisting of a large bias resistor and a normal metal - superconductor tunnel junction (NIS). The effective Coulomb blockade of the JJ can be controlled by the tunneling current through the NIS junction leading to transistor-like characteristics. We show using phase correlation theory and numerical simulations that substantial current gain with low current resolution (< 0.1 fA) and noise temperature (< 0.1 K) can be achieved. Good agreement between our numerical simulations and experimental results is obtained.

  5. Universal Time Tunneling

    OpenAIRE

    Nimtz, Guenter

    2009-01-01

    How much time does a tunneling wave packet spent in traversing a barrier? Quantum mechanical calculations result in zero time inside a barrier . In the nineties analogous tunneling experiments with microwaves were carried out. The results agreed with quantum mechanical calculations. Electron tunneling time is hard to measure being extremely short and parasitic effects due to the electric charge of electrons may be dominant. However, quite recently the atomic ionization tunne...

  6. Electronic Resources Evaluation Central: Using Off-the-Shelf Software, Web 2.0 Tools, and LibGuides to Manage an Electronic Resources Evaluation Process

    Science.gov (United States)

    England, Lenore; Fu, Li

    2011-01-01

    A critical part of electronic resources management, the electronic resources evaluation process is multi-faceted and includes a seemingly endless range of resources and tools involving numerous library staff. A solution is to build a Web site to bring all of the components together that can be implemented quickly and result in an organizational…

  7. Simulation of electron transmittance and tunnel current in n+ Poly-Si/HfSiOxN/Trap/SiO2/Si(100) capacitors using analytical and numerical approaches

    Science.gov (United States)

    Noor, Fatimah A.; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal

    2015-04-01

    In this paper, we discuss the electron transmittance and tunneling current in high-k-based-MOS capacitors with trapping charge by including the off-diagonal effective-mass tensor elements and the effect of coupling between transverse and longitudinal energies represented by an electron velocity in the gate. The HfSiOxN/SiO2 dual ultrathin layer is used as the gate oxide in an n+ poly- Si/oxide/Si capacitor to replace SiO2. The main problem of using HfSiOxN is the charge trapping formed at the HfSiOxN/SiO2 interface that can influence the performance of the device. Therefore, it is important to develop a model taking into account the presence of electron traps at the HfSiOxN/SiO2 interface in the electron transmittance and tunneling current. The transmittance and tunneling current in n+ poly- Si/HfSiOxN/trap/SiO2/Si(100) capacitors are calculated by using Airy wavefunctions and a transfer matrix method (TMM) as analytical and numerical approaches, respectively. The transmittance and tunneling current obtained from the Airy wavefunction are compared to those computed by the TMM. The effects of the electron velocity on the transmittance and tunneling current are also discussed.

  8. Next Generation Networks for Distributed Electronic Resources: Opportunities and Challenges

    OpenAIRE

    Soysal, Murat

    2014-01-01

    The changes in the lifestyle of the people, new applications, technological developments and the telecommunication market drive the adoption Next Generation Network (NGN) as the new network architecture. NGN has a service-centric architecture which promotes agile creation of services and then maintenance of these services with end-to-end QoS support. In the current era, every internet user is a potential electronic resource user. Due to the transition from the traditional mode of collect...

  9. Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises

    Science.gov (United States)

    Shao, Fang

    The paper discussed electronic-commerce's influence on enterprise human resources management, proposed and proved the human resources management strategy which electronic commerce enterprise should adopt from recruitment strategy to training strategy, keeping talent strategy and other ways.

  10. Calculations of the radiation doses to the electronic equipment and magnet coil insulation in the PEP-II tunnel

    International Nuclear Information System (INIS)

    The PEP-II collaboration is a new physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a low-energy positron ring (4 GeV, called the LER) atop a high-energy electron ring (10 GeV, called the HER). Both rings are being designed to permit a high circulating current of 3 A, corresponding to a beam particle number of 1.38x1014. Dose calculations were made to estimate the potential for radiation damages to the electronics and magnet coil insulation in the arc section of the tunnel. An analytical code, SHIELD11, was used to calculate the dose from photon and neutron radiations resulting from beam losses in various modes of operation. Several EGS4 Monte Carlo user codes were developed to calculate the dose from the synchrotron radiation escaping the vacuum chamber in stored beam mode. Two different LER vacuum chamber designs were studied: a 0.35-cm-thick copper wall chamber and a 1-cm-thick aluminum wall chamber with a copper absorber 6 m downstream of every dipole to absorb the synchrotron radiation in a local spot. The HER has a 0.5-cm-thick copper vacuum chamber. Shielding from the 5.4-m-long, C-shaped iron bending magnet for the HER was considered for the beam radiation, while no other structural shielding was assumed for the LER. Furthermore, the dose from all radiations scattering back from the tunnel concrete wall were also estimated using the albedo method or the MORSE code. The results of the dose estimations arde. The results of the dose estimations are presented. (orig.)

  11. Direct observation of electron emission from the grain boundaries of chemical vapour deposition diamond films by tunneling atomic force microscopy

    International Nuclear Information System (INIS)

    The emission of electrons from diamond in vacuum occurs readily as a result of the negative electron affinity of the hydrogenated surface due to features with nanoscale dimensions, which can concentrate electric fields high enough to induce electron emission from them. Electrons can be emitted as a result of an applied electric field (field emission) with possible uses in displays or cold-cathode devices. Alternatively, electrons can be emitted simply by heating the diamond in vacuum to temperatures as low as 350?°C (thermionic emission), and this may find applications in solar energy generation or energy harvesting devices. Electron emission studies usually use doped polycrystalline diamond films deposited onto Si or metallic substrates by chemical vapor deposition, and these films have a rough, faceted morphology on the micron or nanometer scale. Electron emission is often improved by patterning the diamond surface into sharp points or needles, the idea being that the field lines concentrate at the points lowering the barrier for electron emission. However, there is little direct evidence that electrons are emitted from these sharp tips. The few reports in the literature that have studied the emission sites suggested that emission came from the grain boundaries and not the protruding regions. We now present direct observation of the emission sites over a large area of polycrystalline diamond using tunneling atomic force microscopy. We confirm that the emission current comes mostly from the grain boundaries, which is consistent with a model for emission in which the non-diamond phase is the source of electrons with a threshold that is determined by the surrounding hydrogenated diamond surface

  12. Direct observation of electron emission from the grain boundaries of chemical vapour deposition diamond films by tunneling atomic force microscopy

    Science.gov (United States)

    Chatterjee, Vijay; Harniman, Robert; May, Paul W.; Barhai, P. K.

    2014-04-01

    The emission of electrons from diamond in vacuum occurs readily as a result of the negative electron affinity of the hydrogenated surface due to features with nanoscale dimensions, which can concentrate electric fields high enough to induce electron emission from them. Electrons can be emitted as a result of an applied electric field (field emission) with possible uses in displays or cold-cathode devices. Alternatively, electrons can be emitted simply by heating the diamond in vacuum to temperatures as low as 350 °C (thermionic emission), and this may find applications in solar energy generation or energy harvesting devices. Electron emission studies usually use doped polycrystalline diamond films deposited onto Si or metallic substrates by chemical vapor deposition, and these films have a rough, faceted morphology on the micron or nanometer scale. Electron emission is often improved by patterning the diamond surface into sharp points or needles, the idea being that the field lines concentrate at the points lowering the barrier for electron emission. However, there is little direct evidence that electrons are emitted from these sharp tips. The few reports in the literature that have studied the emission sites suggested that emission came from the grain boundaries and not the protruding regions. We now present direct observation of the emission sites over a large area of polycrystalline diamond using tunneling atomic force microscopy. We confirm that the emission current comes mostly from the grain boundaries, which is consistent with a model for emission in which the non-diamond phase is the source of electrons with a threshold that is determined by the surrounding hydrogenated diamond surface.

  13. Direct observation of electron emission from the grain boundaries of chemical vapour deposition diamond films by tunneling atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Vijay [School of Chemistry, University of Bristol, Cantock' s Close, Bristol BS8 1TS (United Kingdom); Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835215 (India); Harniman, Robert; May, Paul W., E-mail: paul.may@bristol.ac.uk [School of Chemistry, University of Bristol, Cantock' s Close, Bristol BS8 1TS (United Kingdom); Barhai, P. K. [Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835215 (India)

    2014-04-28

    The emission of electrons from diamond in vacuum occurs readily as a result of the negative electron affinity of the hydrogenated surface due to features with nanoscale dimensions, which can concentrate electric fields high enough to induce electron emission from them. Electrons can be emitted as a result of an applied electric field (field emission) with possible uses in displays or cold-cathode devices. Alternatively, electrons can be emitted simply by heating the diamond in vacuum to temperatures as low as 350?°C (thermionic emission), and this may find applications in solar energy generation or energy harvesting devices. Electron emission studies usually use doped polycrystalline diamond films deposited onto Si or metallic substrates by chemical vapor deposition, and these films have a rough, faceted morphology on the micron or nanometer scale. Electron emission is often improved by patterning the diamond surface into sharp points or needles, the idea being that the field lines concentrate at the points lowering the barrier for electron emission. However, there is little direct evidence that electrons are emitted from these sharp tips. The few reports in the literature that have studied the emission sites suggested that emission came from the grain boundaries and not the protruding regions. We now present direct observation of the emission sites over a large area of polycrystalline diamond using tunneling atomic force microscopy. We confirm that the emission current comes mostly from the grain boundaries, which is consistent with a model for emission in which the non-diamond phase is the source of electrons with a threshold that is determined by the surrounding hydrogenated diamond surface.

  14. A Two-Dimensional Electron Gas as a Sensitive Detector for Time-Resolved Tunneling Measurements on Self-Assembled Quantum Dots

    Directory of Open Access Journals (Sweden)

    Reuter Dirk

    2010-01-01

    Full Text Available Abstract A two-dimensional electron gas (2DEG situated nearby a single layer of self-assembled quantum dots (QDs in an inverted high electron mobility transistor (HEMT structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-time conductance measurements in combination with an boxcar-like evaluation method enables us to unambiguously identify the transients as tunneling events between the s- and p-electron QD states and the 2DEG and rule out defect-related transients.

  15. Time-dependent exchange and tunneling: detection at the same place of two electrons emitted simultaneously from different sources.

    Science.gov (United States)

    Marian, D; Colomés, E; Oriols, X

    2015-06-24

    Two-particle scattering probabilities in tunneling scenarios with exchange interaction are analyzed with quasi-particle wave packets. Two initial one-particle wave packets (with opposite central momentums) are spatially localized at each side of a barrier. After impinging upon a tunneling barrier, each wave packet splits into transmitted and reflected components. When the initial two-particle anti-symmetrical state is defined as a Slater determinant of any type of (normalizable) one-particle wave packet, it is shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. In some particular scenarios, the transmitted and reflected components become orthogonal and the mentioned probabilities reproduce those values associated to distinguishable particles. These unexpected non-zero probabilities are still present when non-separable Coulomb interaction or non-symmetrical potentials are considered. On the other hand, for initial wave packets close to Hamiltonian eigenstates, the usual zero two-particle probability for electrons at the same side of the barrier found in the literature is recovered. The generalization to many-particle scattering probabilities with quasi-particle wave packets for low and high phase-space density are also analyzed. The far-reaching consequences of these non-zero probabilities in the accurate evaluation of quantum noise in mesoscopic systems are briefly indicated. PMID:26030519

  16. Time-dependent exchange and tunneling: detection at the same place of two electrons emitted simultaneously from different sources

    Science.gov (United States)

    Marian, D.; Colomés, E.; Oriols, X.

    2015-06-01

    Two-particle scattering probabilities in tunneling scenarios with exchange interaction are analyzed with quasi-particle wave packets. Two initial one-particle wave packets (with opposite central momentums) are spatially localized at each side of a barrier. After impinging upon a tunneling barrier, each wave packet splits into transmitted and reflected components. When the initial two-particle anti-symmetrical state is defined as a Slater determinant of any type of (normalizable) one-particle wave packet, it is shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. In some particular scenarios, the transmitted and reflected components become orthogonal and the mentioned probabilities reproduce those values associated to distinguishable particles. These unexpected non-zero probabilities are still present when non-separable Coulomb interaction or non-symmetrical potentials are considered. On the other hand, for initial wave packets close to Hamiltonian eigenstates, the usual zero two-particle probability for electrons at the same side of the barrier found in the literature is recovered. The generalization to many-particle scattering probabilities with quasi-particle wave packets for low and high phase-space density are also analyzed. The far-reaching consequences of these non-zero probabilities in the accurate evaluation of quantum noise in mesoscopic systems are briefly indicated.

  17. The calculation of the conductance and electron tunneling characteristic time from metal-molecule contact in a molecular wire

    Directory of Open Access Journals (Sweden)

    S. A. Ketabi

    2003-12-01

    Full Text Available   In this paper, on the basis of tight-binding model and a generalized Green- function method as well as Lanczos algorithm procedure, the effects of the metal-molecule coupling(MMC strength on the electronic transmission through a metal-single molecule-metal(MMM system is investigated. Using the Landauer formalism we study some of the significant conductance properties of this system as a molecular wire. Our results show that with the increase of the length of the molecule, the conductance of the molecular wire decreases exponentially. With trans-polyacetylene (trans-PA as the molecule, we calculate a characteristic time for electron transmission through the MMM system. This time scale measures the delay caused by tunneling through the MMC. Our calculations show that the conductance is sensitive to the MMC strength. The focus is on the significant relationship between this time scale and the strength of the metal-molecule(trans-PA coupling.

  18. SAGES Update: Electronic Disease Surveillance in Resource-Limited Settings

    Science.gov (United States)

    Sheri, Lewis L.; Campbell, Timothy C.; Coberly, Jacqueline S.; Wojcik, Richard A.; Patel, Shraddha V.; Feighner, Brian

    2013-01-01

    Objective The Suite for Automated Global Electronic bioSurveillance (SAGES) is a collection of modular, flexible, open-source software tools for electronic disease surveillance in resource-limited settings. This demonstration will illustrate several new innovations and update attendees on new users in Africa and Asia. Introduction The new 2005 International Health Regulations (IHR), a legally binding instrument for all 194 WHO member countries, significantly expanded the scope of reportable conditions and are intended to help prevent and respond to global public health threats. SAGES aims to improve local public health surveillance and IHR compliance with particular emphasis on resource-limited settings. More than a decade ago, in collaboration with the US Department of Defense (DoD), the Johns Hopkins University Applied Physics Laboratory (JHU/APL) developed the Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE). ESSENCE collects, processes, and analyzes non-traditional data sources (i.e. chief complaints from hospital emergency departments, school absentee data, poison control center calls, over-the-counter pharmaceutical sales, etc.) to identify anomalous disease activity in a community. The data can be queried, analyzed, and visualized both temporally and spatially by the end user. The current SAGES initiative leverages the experience gained in the development of ESSENCE, and the analysis and visualization components of SAGES are built with the same features in mind. Methods SAGES tools are organized into four categories: 1) data collection, 2) analysis & visualization, 3) communications, and 4) modeling/simulation/evaluation. Within each category, SAGES offers a variety of tools compatible with surveillance needs and different types or levels of information technology infrastructure. SAGES tools are built in a modular nature, which allows for the user to select one or more tools to enhance an existing surveillance system or use the tools en masse for an end-to-end electronic disease surveillance capability. Thus, each locality can select tools from SAGES based upon their needs, capabilities, and existing systems to create a customized electronic disease surveillance system. New OpenESSENCE developments include improved data query ability, improved mapping functionality, and enhanced training materials. New cellular phone developments include the ability to concatenate single SMS messages sent by simple or Smart Android cell phones. This ‘multiple-SMS’ message ability allows use of SMS technology to send and receive health information exceeding normal SMS message length in a manner transparent to the users. Conclusions The SAGES project is intended to enhance electronic disease surveillance capacity in resource-limited settings around the world. We have combined electronic disease surveillance tools developed at JHU/APL with other freely-available, interoperable software tools to create SAGES. We believe this suite of tools will facilitate local and regional electronic disease surveillance, regional public health collaborations, and international disease reporting. SAGES development, funded by the US Armed Forces Health Surveillance Center, continues as we add new international collaborators. SAGES tools are currently deployed in locations in Africa, Asia and South America, and are offered to other interested countries around the world.

  19. Electronic band alignment and electron transport in Cr/BaTiO3/Pt ferroelectric tunnel junctions

    International Nuclear Information System (INIS)

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO3(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO3/Pt junctions with a sub-?m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ?30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO3/Pt (Cr/BaTiO3) interface +0.42(?0.03) eV following downward to upward polarization reversal.

  20. Electronic band alignment and electron transport in Cr/BaTiO{sub 3}/Pt ferroelectric tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Zenkevich, A. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Minnekaev, M.; Matveyev, Yu.; Lebedinskii, Yu. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Bulakh, K.; Chouprik, A.; Baturin, A. [Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Maksimova, K. [Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Thiess, S.; Drube, W. [Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg (Germany)

    2013-02-11

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO{sub 3}(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO{sub 3}/Pt junctions with a sub-{mu}m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of {approx}30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO{sub 3}/Pt (Cr/BaTiO{sub 3}) interface +0.42(-0.03) eV following downward to upward polarization reversal.

  1. Modeling of Electronic Transport in Scanning Tunneling Microscope Tip-Carbon Nanotube Systems

    Science.gov (United States)

    Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

    2000-01-01

    A model is proposed for two observed current-voltage (I-V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube. We claim that there are two mechanical contact modes for a tip (metal) -nanotube (semiconductor) junction (1) with or (2) without a tiny vacuum gap (0.1 - 0.2 nm). With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V nanotube, and the bias polarities would be reversed for a p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type.

  2. Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve

    Directory of Open Access Journals (Sweden)

    Ma Jing-Min

    2011-01-01

    Full Text Available Abstract Spin-dependent transport through a quantum-dot (QD ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively. PACS numbers:

  3. Observation of Squeezing in the Electron Quantum Shot Noise of a Tunnel Junction

    Science.gov (United States)

    Gasse, Gabriel; Lupien, Christian; Reulet, Bertrand

    2013-09-01

    We report the measurement of the fluctuations of the two quadratures of the electromagnetic field generated by a quantum conductor, a dc- and ac-biased tunnel junction placed at very low temperature. We observe that the variance of the fluctuations on one quadrature can go below that of vacuum, i.e., that the radiated field is squeezed. This demonstrates the quantum nature of the radiated electromagnetic field.

  4. Observation of Squeezing in the Electron Quantum Shot Noise of a Tunnel Junction

    OpenAIRE

    Gasse, Gabriel; Lupien, Christian; Reulet, Bertrand

    2013-01-01

    We report the measurement of the fluctuations of the two quadratures of the electromagnetic field generated by a quantum conductor, a dc- and ac-biased tunnel junction placed at very low temperature.We observe that the variance of the fluctuations on one quadrature can go below that of vacuum, i.e., that the radiated field is squeezed. This demonstrates the quantum nature of the radiated electromagnetic field.

  5. Electronic Document Management: A Human Resource Management Case Study

    Directory of Open Access Journals (Sweden)

    Thomas Groenewald

    2004-11-01

    Full Text Available This case study serve as exemplar regarding what can go wrong with the implementation of an electronic document management system. Knowledge agility and knowledge as capital, is outlined against the backdrop of the information society and knowledge economy. The importance of electronic document management and control is sketched thereafter. The literature review is concluded with the impact of human resource management on knowledge agility, which includes references to the learning organisation and complexity theory. The intervention methodology, comprising three phases, follows next. The results of the three phases are presented thereafter. Partial success has been achieved with improving the human efficacy of electronic document management, however the client opted to discontinue the system in use. Opsomming
    Die gevalle studie dien as voorbeeld van wat kan verkeerd loop met die implementering van ’n elektroniese dokumentbestuur sisteem. Teen die agtergrond van die inligtingsgemeenskap en kennishuishouding word kennissoepelheid en kennis as kapitaal bespreek. Die literatuurstudie word afgesluit met die inpak van menslikehulpbronbestuur op kennissoepelheid, wat ook die verwysings na die leerorganisasie en kompleksietydsteorie insluit. Die metodologie van die intervensie, wat uit drie fases bestaan, volg daarna. Die resultate van die drie fases word vervolgens aangebied. Slegs gedeelte welslae is behaal met die verbetering van die menslike doeltreffendheid ten opsigte van elektroniese dokumentbestuur. Die klient besluit egter om nie voort te gaan om die huidige sisteem te gebruik nie.

  6. COLLECTIONS OF ELECTRONIC INFORMATION RESOURCES AND THEIR METADESCRIPTIONS AS COMPONENTS OF SCIENTIFIC ELECTRONIC LIBRARY ???????? ??????????? ????????????? ???????? ? ?? ????????? ?? ?????????? ???????? ??????????? ?????????

    Directory of Open Access Journals (Sweden)

    ?.?. ????????

    2011-02-01

    Full Text Available The article presents the results of scientific research components of digital libraries, the main ones being the collection of electronic scientific information resources. An important specific characteristics of collections of scientific information resources, resources of their formation, structure collections, methods of their organization, technology creation, support and use of scientific collections, the role and function of metadata in collections and metadata management technology are represented. On the stage of planning and introduction of scientific e-libraries there can be used results of researches presented in the article, namely: chart of forming of collections of scientific informative resources; stages of planning and development of metadescriptions, and similarly the use of standard the Dublin kernel, creation of metadescriptions.? ?????? ?????? ?????????? ??????????? ????????? ???????? ??????????? ?????????, ????????? ? ???? ? ???????? ???????? ??????????? ????????????? ????????. ???????? ???????????? ?????????? ??????????? ???????? ???????? ????????????? ????????, ??????? ?? ??????????, ????????? ????????, ?????? ?? ??????????????, ?????????? ?????????, ???????????? ????????? ?? ???????????? ???????? ????????; ???? ? ??????? ????????? ? ????????? ? ?????????? ?????????? ??????????. ?? ????? ???????????? ? ???????????? ???????? ??????????? ????????? ?????? ???? ??????????? ?????????? ???????????, ????????? ? ??????, ? ????: ????? ?????????? ???????? ???????? ????????????? ????????; ????? ???????????? ? ???????? ?????????? ? ???????????? ????????? ?????????? ????, ????????? ??????????.

  7. Modeling of electronic states in low-temperature-grown gallium arsenide and conduction properties of tunneling based contact

    Science.gov (United States)

    Chen, Nien-Po

    2001-07-01

    A set of defect distribution models for un-annealed low-temperature-grown GaAs (LTG:GaAs) are developed, based on experimental observations with scanning tunneling spectroscopy, incorporating the Coulomb gap and Hubbard correlation in the distribution of the density of states. The models are tested against independent experiments on bulk resistivity and surface electric field. With the models as the foundation, the conduction models are developed for nonalloyed ohmic contacts, in micron-scale and nanometer-scale, to n-type GaAs (n-GaAs) which employ a surface layer of LTG:GaAs. For the micron-scale ohmic contact, the conduction model has been used to fit measured rhoc versus LTG:GaAs layer thickness and versus measurement temperature. These comparisons provide insights into the contact mechanism (electron tunneling between metal states and conduction band states in n-GaAs) and indicate that low potential barrier heights (due to un-pinned surface Fermi level) and the high density of activated donors (˜1020 cm-3) in n++ GaAs have been achieved in these ex situ contacts. For the nanometer-scale ohmic contact, the conduction model is based on the sequential tunneling through two barriers---in xylyl dithiol molecules and in LTG:GaAs/n++GaAs depletion region---with part of LTG:GaAs midgap defect band in between. The model has been used to fit rho c versus undoped and Be-doped contacts. It shows quantitatively that the abundance of the available states around the Fermi level in Be-doped case contributes to the superior contact performance.

  8. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules : a prediction from theory

    DEFF Research Database (Denmark)

    JØrgensen, Jacob Lykkebo; Gagliardi, Alessio

    2013-01-01

    Cross-conjugated molecules are known to exhibit destructive quantum interference, a property that has recently received considerable attention in single-molecule electronics. Destructive quantum interference can be understood as an antiresonance in the elastic transmission near the Fermi energy and leading to suppressed levels of elastic current. In most theoretical studies, only the elastic contributions to the current are taken into account. In this paper, we study the inelastic contributions to the current in cross-conjugated molecules and find that while the inelastic contribution to the current is larger than for molecules without interference, the overall behavior of the molecule is still dominated by the quantum interference feature. Second, an ongoing challenge for single molecule electronics is understanding and controlling the local geometry at the molecule-surface interface. With this in mind, we investigate a spectroscopic method capable of providing insight into these junctions for cross-conjugated molecules: inelastic electron tunneling spectroscopy (IETS). IETS has the advantage that the molecule interface is probed directly by the tunneling current. Previously, it has been thought that overtones are not observable in IETS. Here, overtones are predicted to be strong and, in some cases, the dominant spectroscopic features. We study the origin of the overtones and find that the interference features in these molecules are the key ingredient. The interference feature is a property of the transmission channels of the ? system only, and consequently, in the vicinity of the interference feature, the transmission channels of the ? system and the ? system become equally transmissive. This allows for scattering between the different transmission channels, which serves as a pathway to bypass the interference feature. A simple model calculation is able to reproduce the results obtained from atomistic calculations, and we use this to interpret these findings.

  9. Infrared catastrophe and tunneling into strongly correlated electron systems: Exact solution of the x-ray edge limit for the 1D electron gas and 2D Hall fluid

    OpenAIRE

    Patton, Kelly R.; Geller, Michael R.

    2005-01-01

    In previous work we have proposed that the non-Fermi-liquid spectral properties in a variety of low-dimensional and strongly correlated electron systems are caused by the infrared catastrophe, and we used an exact functional integral representation for the interacting Green's function to map the tunneling problem onto the x-ray edge problem, plus corrections. The corrections are caused by the recoil of the tunneling particle, and, in systems where the method is applicable, a...

  10. Local opening of a large bandgap in metallic single-walled carbon nanotubes induced by tunnel injection of low-energy electrons

    International Nuclear Information System (INIS)

    Probing with a tip of scanning tunneling microscopy (STM) of metallic single-walled carbon nanotubes (SWCNT) was found to induce defects in the tubes. The primary defect formation by probing was enhanced with a rate proportional to tunnel-injected electron current above a sample-bias threshold of around +4 V. Scanning tunneling spectroscopic measurements of local density of states revealed that the defects imaged by STM, presumably secondary defects stabilized at the test temperature (95 K), are accompanied by a localized bandgap of 0.7 eV, which may account for the reported metal-semiconductor conversion in SWCNT-based field-effect transistor that is induced by low-energy electron irradiation.

  11. Combined action of the bound-electron nonlinearity and the tunnel-ionization current in low-order harmonic generation in noble gases

    CERN Document Server

    Sapaev, U; Herrmann, J

    2013-01-01

    We study numerically low-order harmonic generation in noble gases pumped by intense femtosecond laser pulses in the tunneling ionization regime. We analyze the influence of the phase-mismatching on this process, caused by the generated plasma, and study in dependence on the pump intensity the origin of harmonic generation arising either from the bound-electron nonlinearity or the tunnel-ionization current. It is shown that in argon the optimum pump intensity of about 100 TW/cm$^2$ leads to the maximum efficiency, where the main contribution to low-order harmonics originates from the bound-electron third and fifth order susceptibilities, while for intensities higher than 300 TW/cm$^2$ the tunnel-ionization current plays the dominant role. Besides, we predict that VUV pulses at 133 nm can be generated with relatively high efficiency of about $1.5\\times10^{-3}$ by 400 nm pump pulses.

  12. Electronic and Magnetic Properties of Surface-Supported Hydrocarbon Radicals Studied by Low-Temperature Scanning Tunneling Microscopy

    International Nuclear Information System (INIS)

    Full text: The competition between screening of local spins and magnetic interactions of neighbouring spins determines many of the electronic and magnetic properties of dilute magnetic systems. We report on low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments performed on linear chains of surface-supported hydrocarbon spin-1/2 radicals. The spin chains are prepared by self-assembly of the stable sp magnetic radicals a,g-bisdiphenylene-b-phenylallyl (BDPA) on a single-crystal metal surface under ultrahigh vacuum conditions. Below about 50 K the chains exhibit many of the characteristic properties of the Kondo effect observed by STM-based electron transport experiments at the atomic scale. We find strong evidence for a parallel alignment of neighbouring spins within the chains mediated by the electron gas of the supporting metal substrate. Spectroscopic imaging of radical chains reveals extended two-dimensional Kondo patterns. They span several nm2 across the substrate area even into regions of the pristine Au substrate, indicating the involvement of surface-state electrons from the substrate. The single adsorbed radicals exhibit a handedness as revealed by topographic STM imaging at the single-molecule level, which leads to an enantio-selective chain growth and the formation of structurally different domains of neighboring radical chains. (author)

  13. Evidence from inelastic electron tunnelling spectroscopy for vibrational mode reassignments in simple aliphatic carboxylate ions

    Science.gov (United States)

    Walmsley, D. G.; Nelson, W. J.; Brown, N. M. D.; de Cheveigné, S.; Gauthier, S.; Klein, J.; Léger, A.

    Tunnelling studies of the vibrational spectra of formate- and acetate-, including 18O-enriched acetate-, anions adsorbed on plasma-grown aluminium and magnesium oxide surfaces show that the CO 2- symmetric stretch mode can be clearly distinguished from the CH modes in the same region of the spectra. This CO 2- mode of the formate ion is at 1456 cm -1 on aluminium oxide and at 1348 cm -1 on magnesium oxide; for the acetate ion the corresponding values are 1463 and 1445 cm -1

  14. Electronic-state-controlled reset operation in quantum dot resonant-tunneling single-photon detectors

    International Nuclear Information System (INIS)

    The authors present a systematic study of an introduced reset operation on quantum dot (QD) single photon detectors operating at 77?K. The detectors are based on an AlAs/GaAs/AlAs double-barrier resonant tunneling diode with an adjacent layer of self-assembled InAs QDs. Sensitive single-photon detection in high (dI)/(dV) region with suppressed current fluctuations is achieved. The dynamic detection range is extended up to at least 104 photons/s for sensitive imaging applications by keeping the device far from saturation by employing an appropriate reset frequency

  15. Electronic properties of Al-SiO2-(n or p) Si MIS tunnel diodes

    OpenAIRE

    Vuillod, J.; Pananakakis, G.

    1985-01-01

    Automatic measurements I-V, C/G(V, ?) are used to study the electrical properties of a great number of aluminum-SiO 2-n or p type silicon MIS tunnel diodes with an oxide thickness of 30 Å prepared by two technologies of oxidation, low pressure chemical vapour deposition (LPCVD) and low oxygen pressure (LPO2). A comparison between the I-V and C-V characteristics on n and p substrate is presented as well as a dispersion study of I-V characteristics. The modelling of I-V characteristics has be...

  16. Study on the interface thermal stability of metal-oxide-semiconductor structures by inelastic electron tunneling spectroscopy

    Science.gov (United States)

    Huang, Chih-Feng; Tsui, Bing-Yue; Tzeng, Pei-Jer; Lee, Lurng-Shehng; Tsai, Ming-Jinn

    2006-06-01

    The bias polarity-dependent inelastic electron tunneling spectroscopy is employed to detect the thermal stability of the Ta -Pt/SiO2/Si and Ta -Pt/HfO2/Si structures. This work provides a direct evidence that the Fermi-level pinning of metal gates is counted for the generation of extrinsic states due to interface interaction. A Ta2O5 layer forms at the Ta -Pt/SiO2 interface during thermal annealing whereas only an intermittent Ta-O bond is observed at the Ta -Pt/HfO2 interface. Although the heat of formation of HfO2 is lower than that of SiO2, Si presumably diffuses into HfO2 layer and replaces Hf atoms during the high-temperature annealing.

  17. Electron tunnelling into superconducting filaments: depth profiling the energy gap of NbTi filaments from magnet wires

    International Nuclear Information System (INIS)

    Squeezable electron tunneling (SET) junctions consisting of superconducting NbTi filaments (extracted from magnet wires) and sputtered Nb thinfilm counter electrodes were used to determine the energy gap at the surface of the filaments. The current versus voltage curves of junctions immersed in liquid helium at 4 K were measured for a series of filaments taken from the same wire. Each filament had been etched to remove a surface layer of varying thickness so that the energy gap could be determined as a function of depth into the surface of an ''average'' filament. It was found that some manufacturing processes yield filaments having surface layers with reduced energy gaps of 0.4 meV compared to measured interior bulk values ranging from 1.2 to 1.3 meV

  18. Electronic properties of nanoporous TiO2 films investigated in real space by means of scanning tunnelling spectroscopy

    International Nuclear Information System (INIS)

    Nanoporous TiO2 films with a thickness between 100 nm and 8 ?m were studied by scanning tunnelling spectroscopy. The bias voltage of significantly increased differential conductivity, indicating the conduction and valence bands, was found to be strongly dependent on layer thickness and the underlying substrate material. This effect is traced back to the high resistivity of the oxide films and the formation of Schottky barriers at the TiO2-substrate contact. All films showed a strong hysteresis as a function of sweep direction of the bias voltage pointing towards the existence of a high number of localized electronic trap states. This effect is getting even more pronounced upon sample ageing. Laterally resolved measurements show that the major part of the surface exhibits similar I(V) characteristics with minor deviations, while smaller areas with significantly different response are identified. These areas are comparable in size to the individual crystals the material is composed of

  19. Nanolithography by non-contact AFM induced local oxidation Fabrication of tunneling barriers suitable for single electron devices

    CERN Document Server

    Irmer, B; Lorenz, H; Kotthaus, J P

    1998-01-01

    We study local oxidation induced by dynamic atomic force microscopy (AFM), commonly called TappingMode AFM. This minimizes the field induced forces, which cause the tip to blunt, and enables us to use very fine tips. We are able to fabricate Ti/TiOx line grids with 18 nm period and well defined isolating barriers as small as 15 nm. These junctions show a non-linear current-voltage characteristic and an exponential dependence of the conductance on the oxide width, indicating tunneling as the dominant conduction mechanism. From the conductance - barrier width dependence we derive a barrier height of 178 meV. Numerical calculations of the lateral field distribution for different tip geometries allow to design the optimum tip for the most localised electric field. The electron-beam-deposition (EBD) technique makes it possible to actually produce tips of the desired geometry.

  20. Visualizing electron correlation by means of ab initio scanning tunneling spectroscopy images of single molecules

    Science.gov (United States)

    Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

    2011-01-01

    Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many-body effects to the molecular world as well. In this paper, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard quantum chemical methods to calculate the quantities necessary to provide the "correlated" STM molecular image. The developed approach has been applied to 18 different molecules to explore the effects of their chemical nature and of their substituents, as well as to verify the possible contribution by transition metal centers. Whereas the bulk of calculations has been performed with the configuration interaction method with single and double excitations (CISD), because of the computational cost some tests have been also performed with the more accurate coupled cluster with single and double excitations (CCSD) method to quantify the importance of the computational level on many-body STM images. We have found that correlation induces a remarkable squeezing of the images, and that correlated images are not derived from Hartree-Fock HOMO or LUMO alone, but include contributions from other orbitals as well. Although correlation effects are too small to be resolved by present STM experiments for the studied molecules, our results provide hints for seeking out other species with larger, and possibly experimentally detectable, correlation effects.

  1. Comparison of Resource Requirements for a Wind Tunnel Test Designed with Conventional vs. Modern Design of Experiments Methods

    Science.gov (United States)

    DeLoach, Richard; Micol, John R.

    2011-01-01

    The factors that determine data volume requirements in a typical wind tunnel test are identified. It is suggested that productivity in wind tunnel testing can be enhanced by managing the inference error risk associated with evaluating residuals in a response surface modeling experiment. The relationship between minimum data volume requirements and the factors upon which they depend is described and certain simplifications to this relationship are realized when specific model adequacy criteria are adopted. The question of response model residual evaluation is treated and certain practical aspects of response surface modeling are considered, including inference subspace truncation. A wind tunnel test plan developed by using the Modern Design of Experiments illustrates the advantages of an early estimate of data volume requirements. Comparisons are made with a representative One Factor At a Time (OFAT) wind tunnel test matrix developed to evaluate a surface to air missile.

  2. Resistivity of thin gold films on mica induced by electron-surface scattering: Application of quantitative scanning tunneling microscopy

    International Nuclear Information System (INIS)

    We report a comparison between the resistivity measured on thin gold films deposited on mica, with predictions based upon classical theories of size effects (Drude's, Sondheimer's and Calecki's), as well as predictions based upon quantum theories of electron-surface scattering (the modified theory of Sheng, Xing and Wang, the theory of Tesanovic, Jaric and Maekawa, and that of Trivedi and Aschroft). From topographic images of the surface recorded with a Scanning Tunneling Microscope, we determined the rms roughness amplitude, ? and the lateral correlation length, ? corresponding to a Gaussian representation of the average height-height autocorrelation function, describing the roughness of each sample in the scale of length set by the Fermi wave length. Using (?, ?) as input data, we present a rigorous comparison between resistivity data and predictions based upon the theory of Calecki as well as quantum theoretical predictions without adjustable parameters. The resistivity was measured on gold films of different thickness evaporated onto mica substrates, between 4 K and 300 K. The resistivity data covers the range 0.1 < x(T) < 6.8, for 4 K < T < 300 K, where x(T) is the ratio between film thickness and electron mean free path in the bulk at temperature T. We experimentally identify electron-surface and electron-phonon scattering as the microscopic electron scattering mechanisms giving rise to the macroscopic resistivity. The different theories are all capable of eifferent theories are all capable of estimating the thin film resistivity to an accuracy better than 10%; however the mean free path and the resistivity characterizing the bulk turn out to depend on film thickness. Surprisingly, only the Sondheimer theory and its quantum version, the modified theory of Sheng, Xing and Wang, predict and increase in resistivity induced by size effects that seems consistent with published galvanomagnetic phenomena also arising from electron-surface scattering measured at low temperatures.

  3. Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments

    OpenAIRE

    Le Sueur, H.; Joyez, P.

    2006-01-01

    The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating an STM in a dilution refrigerator we have designed a room temperature tunnel current amplifier having very small back-action on the tunnel contact and allowing to nearly reach the predicted energy resolution...

  4. Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy

    Science.gov (United States)

    Jafri, S. H. M.; Löfås, H.; Fransson, J.; Blom, T.; Grigoriev, A.; Wallner, A.; Ahuja, R.; Ottosson, H.; Leifer, K.

    2013-05-01

    Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra. Electronic supplementary information (ESI) available: Methods and materials. Details of the ab initio calculation of molecular vibrations and inelastic spectra of ODT between two Au electrodes. A model of carrier transport through the molecular junctions. See DOI: 10.1039/c3nr00505d

  5. Research on the Construction and Management of Electronic Resources in PDA Mode

    Directory of Open Access Journals (Sweden)

    Zhong Wenjuan

    2014-01-01

    Full Text Available PDA Patron Driven Acquisitions (PDA is literature resources construction mode dominating by user, it is approved by the user because of getting real-time and purchasing user needs. In this mode, the construction of electronic resources tends to get the required resources at this moment. The librarians face more challenge that how to coordinate the permanent preservation and used in real-time on the construction and management of library electronic resources. The article try to put forward some tactics of electronic resources reasonable construction and standardized management from allocation of funds, adjustment of the resource type, performance evaluation of electronic resources, improving electronic resources management system, building institutional repository, analyzing and mining user data and other aspects.

  6. An electron tunneling study of superconductivity in amorphous Sn(sub 1-x)Cu(sub x) thin films

    Science.gov (United States)

    Naugle, D. G.; Watson, P. W., III; Rathnayaka, K. D. D.

    1995-01-01

    The amorphous phase of Sn would have a superconducting transition temperature near 8 K, much higher than that of crystalline Sn with T(sub c) = 3.5 K. To obtain the amorphous phase, however, it is necessary to use a Sn alloy, usually Cu, and quench condense the alloy films onto a liquid He temperature substrate. Alloying with Cu reduces the superconducting transition temperature almost linearly with Cu concentration with an extrapolation of T(sub c) to zero for x = 0.85. Analysis of the tunneling characteristics between a normal metal electrode with an insulating barrier and superconducting amorphous Sn-Cu films provides detailed information on the changes in the electron-phonon coupling which determines T(sub c) in these alloys. The change from very strong electron-phonon coupling to weak-coupling with the increase in Cu content of amorphous Sn-Cu alloys for the range 0.08 is less than or equal to x is less than or equal to 0.41 is presented and discussed in terms of theories of electron-phonon coupling in disordered metals.

  7. Elektronik Bilgi Kaynaklar?n?n Seçimi / Selection of Electronic Information Resources

    Directory of Open Access Journals (Sweden)

    P?nar Al

    2003-04-01

    Full Text Available For many years, library users have used only from the printed media in order to get the information that they have needed. Today with the widespread use of the Web and the addition of electronic information resources to library collections, the use of information in the electronic environment as well as in printed media is started to be used. In time, such types of information resources as, electronic journals, electronic books, electronic encyclopedias, electronic dictionaries and electronic theses have been added to library collections. In this study, selection criteria that can be used for electronic information resources are discussed and suggestions are provided for libraries that try to select electronic information resources for their collections.

  8. Voltage Dependence of Spin Polarized Tunneling

    CERN Document Server

    Valenzuela, S O; Marcus, C M; Narayanamurti, V; Tinkham, M

    2004-01-01

    A mesoscopic spin valve is used to determine the effective spin polarization of electrons tunneling from and into ferromagnetic transition metals at finite voltages. The tunneling spin polarization from the ferromagnet (FM) slowly decreases with bias, but drops faster and even inverts with voltage when electrons tunnel into it. A bias-dependent free electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the detailed matching of the electron wave function through the tunnel barrier.

  9. Correlated Tunnelling of Two Electrons through a Barrier in Quantum Wires

    CERN Document Server

    Avdonin, S A; Kuperin, Yu A; Rudin, G E; Kuperin, Yu.A.

    2003-01-01

    We study the tunnelling trough a potential barrier of the system of two quantum correlated particles. The system is considered in one dimension. The interaction with the barrier and between particles is approximated by $\\delta$-potentials. Assuming that the particles have the same masses, we reduce the problem to the set of independent planar scattering problems corresponding to two-body flux symmetry with respect to the barrier. In order to solve the problems we apply the method of Sommerfeld-Maluzhinets integral transformation, which requires the solution of a set of functional equations. We show that the sub-problem which is antisymmetric with respect to the center of mass allows the solution in frames of the Bethe ansatz. So we give the exact solution of this problem. For the subproblem which is symmetric we describe the class of solutions for the functional equations and give an approach for obtaining the solution.

  10. Tunneling and migration of the dumbbell defect in electron-irradiated aluminum-zinc alloys

    International Nuclear Information System (INIS)

    Ultrasonic attenuation and velocity measurements on irradiated Al-Zn alloys (0.01, 0.1, and 0.5 at %) indicate a tunneling relaxation of the predominant mixed dumbbell defect at low temperatures, and mixed dumbbell migration at the Stage II anneal temperature. The effect of an internal strain varying with the zinc concentration on the measured decrement and modulus change is striking. Evaluated in the framework of a six-level system, this reveals the simultaneous action of resonance and nonclassical relaxation processes. Using Fe as a probe atom, it is shown that mixed dumbbell dissociation is in an insignificant component of the annealing of this defect. The decrease of the annealing temperature at higher zinc concentrations provides evidence that the mixed dumbbell migrates as a unit during annealing. The energies associated with dumbbell migration and interstitial escape are derived. Further evidence for the migration mechanism is obtained from successive irradiation and annealing

  11. Electronic transport through Fe/MgO/Fe(1 0 0) tunnel junctions

    International Nuclear Information System (INIS)

    The transport properties of Fe/MgO/Fe(1 0 0) tunnel junctions are studied from first principles at finite bias. For parallel alignment of the Fe leads and voltages below 25 mV the current is carried by both majority and minority spins, with the largest contribution coming from the minority. Their transmission is dominated by a sharp resonance through surface states, whose contribution to the current decreases rapidly as the bias increases. The same minority surface state leads to resonant transmission also for the antiparallel alignment of the Fe leads. However, in contrast to the parallel case the resonance is weakly dependent on the bias, leading to a large magnetoresistance at small voltages, which rapidly decreases with increasing voltage and approximately saturates at about 25 mV

  12. Study of the superconducting and phonon properties of the disordered gallium--silver system using electron tunneling techniques

    International Nuclear Information System (INIS)

    Conductance measurements were performed on amorphous gallium junctions with silver impurity concentrations ranging from 0 to 18 at. percent. The superconducting transition temperature was also measured. From analysis of the tunneling curves, the effective phonon spectrum, ?2(?)F(?), and the Coulomb pseudopotential (?*) were calculated. A calculated transition temperature is approximated from the phonon spectrum, using a model for strong-coupling superconductors. For the amorphous Ga(+Ag) junctions there was good agreement between the experimental T/sub C/ values and the corresponding calculated values. The T/sub C/ appears to decrease somewhat linearly with increasing silver impurity concentration. There was likewise a similar linear decrease of the calculated superconducting energy gaps with increasing impurity concentration. From the effective phonon spectra the electron-phonon coupling constant (lambda), the average phonon energy [?], and the average squared phonon energy [?2] all decreased slightly with increasing impurity concentration. The introduction of the impurity silver decreases the electron concentration, and this reduction in electron per atom ratio may be reason for the reduction in T/sub C/ and lambda. Similar measurements and procedures were performed on beta phase structures of selected junctions. Both the transition temperature and calculated energy gap values appear to decrease slightly with increasing silver impurity. Sy with increasing silver impurity. Successful conductance measurements were obtained only for silver impurity concentrations less than 6 at. percent. With this limited range, an analysis of the phonon spectra shows that the electron-phonon coupling constant (lambda) remains essentially constant, while the weighting moments ([?] and [?2]) have decreased slightly with increased silver concentration. The decrease in T/sub C/ with increasing silver impurity is once again attributed to the decreasing electron concentration

  13. A single-electron tunneling reset-set flip-flop

    Energy Technology Data Exchange (ETDEWEB)

    Alencar, Bianca M. S. M. de; Guimarães, Janaina G. [Department of Electrical Engineering, University of Brasilia, Campus Universitário Darcy Ribeiro, Asa Norte, P.O. Box 4386, Brasilia-DF, 70919-970 (Brazil)

    2014-05-15

    In this paper, a new Reset-Set flip-flop fully implemented with single-electron devices is proposed. Its topology derived from NAND gates and was validated at room temperature by simulation. Furthermore, a comparison between the proposed single-electron device and MOS devices in terms of power consumption and occupied area is presented.

  14. Resonant Tunneling in a Dissipative Environment

    OpenAIRE

    Bomze, Yu.; Mebrahtu, H.; Borzenets, I.; Makarovski, A.; Finkelstein, G.

    2010-01-01

    We measure tunneling through a single quantum level in a carbon nanotube quantum dot connected to resistive metal leads. For the electrons tunneling to/from the nanotube, the leads serve as a dissipative environment, which suppresses the tunneling rate. In the regime of sequential tunneling, the height of the single-electron conductance peaks increases as the temperature is lowered, although it scales more weekly than the conventional 1/T. In the resonant tunneling regime (t...

  15. Electronic Safety Resource Tools – Supporting Hydrogen and Fuel Cell Commercialization

    Energy Technology Data Exchange (ETDEWEB)

    Barilo, Nick F.

    2014-09-29

    The Pacific Northwest National Laboratory (PNNL) Hydrogen Safety Program conducted a planning session in Los Angeles, CA on April 1, 2014 to consider what electronic safety tools would benefit the next phase of hydrogen and fuel cell commercialization. A diverse, 20-person team led by an experienced facilitator considered the question as it applied to the eight most relevant user groups. The results and subsequent evaluation activities revealed several possible resource tools that could greatly benefit users. The tool identified as having the greatest potential for impact is a hydrogen safety portal, which can be the central location for integrating and disseminating safety information (including most of the tools identified in this report). Such a tool can provide credible and reliable information from a trustworthy source. Other impactful tools identified include a codes and standards wizard to guide users through a series of questions relating to application and specific features of the requirements; a scenario-based virtual reality training for first responders; peer networking tools to bring users from focused groups together to discuss and collaborate on hydrogen safety issues; and a focused tool for training inspectors. Table ES.1 provides results of the planning session, including proposed new tools and changes to existing tools.

  16. MULER: Building an Electronic Resource Management (ERM) Solution at York University

    OpenAIRE

    Aaron August Lupton; Marcia Kay Salmon

    2012-01-01

    Many university libraries now utilize an Electronic Resource Management (ERM) system to assist with operations related to electronic resources. An ERM is a relational database containing information such as suppliers, costs, holdings, and renewal dates for electronic resources, both at the database and title levels. While commercial ERM products are widely available, some institutions are custom building their own ERM in- house. This article describes how York University in Toronto, Canada, d...

  17. Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells

    International Nuclear Information System (INIS)

    We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures

  18. Electronic phase diagram of NaFe1?xCoxAs investigated by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Our recent scanning tunneling microscopy (STM) studies of the NaFe1?xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe1?xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFe1?xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model. (topical review - iron-based high temperature superconductors)

  19. Non-Equilibrium Green's Function Calculation for Electron Transport through Magnetic Tunnel Junction

    Directory of Open Access Journals (Sweden)

    Sara Nobakht

    2014-06-01

    Full Text Available In this paper non-equilibrium Green's function method –dependent electron transport through non magnetic layer (insulator has been studied in one dimension .electron transport in multi-layer (magnetic/non magnetic/ magneticlayers is studied as quantum .the result show increasing the binding strength of the electrical insulator transition probability density case , the electron density , broad levels of disruption increases. Broad band connection increases the levels of disruption to electrical insulation and show non- conductive insulating state to semiconductor stat and even conductor

  20. Controlled assembly and single electron charging of monolayer protected Au144 clusters: an electrochemistry and scanning tunneling spectroscopy study.

    Science.gov (United States)

    Bodappa, Nataraju; Fluch, Ulrike; Fu, Yongchun; Mayor, Marcel; Moreno-García, Pavel; Siegenthaler, Hans; Wandlowski, Thomas

    2014-12-21

    Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au(144) clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au(144)-MPCs and EC-STS experiments with laterally separated individual Au(144)-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au(144)-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. PMID:25372883

  1. Experimental test of the competition correction for charge capture from the matrix in intermolecular electron tunneling reactions

    International Nuclear Information System (INIS)

    Further experimental tests have been made of a previously presented method to correct for competition for charge capture from the matrix in intermolecular electron transfer (ET) reactions in rigid media. The method is based on a two-step tunneling model which takes into account the correlation between matrix charge capture and intermolecular electron transfer. The goal is to obtain reliable intermolecular ET rates as a function of distance from measurements on rigid solutions containing two randomly distributed solutes. The method should yield the same rate vs. distance function for different donor solute concentrations. Good agreement was obtained by applying the competition correction to pulse radioloysis data for the reaction of the biphenyl anion with 2-methyl-1,4-naphthoquinone in 2-methyltetrahydrofuran (MTHF) at 77 K for donor:acceptor solute concentration ratios of 20:1 to 2:1. Worse agreement was obtained for the reaction of the biphenyl anion with phenanthrene in MTHF, in which case the reaction is slow, and its energetics are substantially influenced by solvation. For such slow reactions, accurate measurements of intermolecular ET rates require donor:acceptor solute concentration ratios so that the donor solute captures most of the matrix charges. Some biphenyl cations are produced by direct ionizations and are stable in frozen MTHF. 14 references, 4 figures, 1 table

  2. Effects of self-affine roughness characteristics on electron transmission through tunneling structures

    International Nuclear Information System (INIS)

    By using the transfer matrix method and the nearly free electron approximation, we investigate effects of interfacial roughness on electron transport through double-barrier quantum wells. The barrier roughness is described by the k-correlation model, and the interface is characterized by the roughness exponent, in-plane correlation length, and root mean square height. Our analysis demonstrates that the transmission probability is sensitive to roughness parameters. Two behaviors are observed for this sensitivity depending on whether the incident wavelength is larger or smaller than the correlation length. - Highlights: ? Electron transmission through quantum wells with interfacial roughness was studied. ? The method was based on transfer matrix method and nearly free-electron approximation. ? The barrier roughness was described by the k-correlation model. ? Transmission probability was studied for different values of roughness parameters. ? Two different behaviors for the effects of roughness on transmission were observed.

  3. Identifying highly conducting Au–C links through inelastic electron tunneling spectroscopy.

    Czech Academy of Sciences Publication Activity Database

    Foti, G.; Vázquez, Héctor; Sanchez-Portal, D.; Arnau, A.; Frederiksen, T.

    2014-01-01

    Ro?. 118, OCT (2014), s. 27106-27112. ISSN 1932-7447 Institutional support: RVO:68378271 Keywords : molecular electronics * alkanes * tin-functionalization * anchoring groups * vibrational spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.835, year: 2013

  4. Resonant tunneling of polarized electrons through nonmagnetic III-V semiconductor multiple barriers

    Scientific Electronic Library Online (English)

    C. Moysés, Araújo; A. Ferreira da, Silva; E. A. de Andrada e, Silva.

    2002-06-01

    Full Text Available The quantum transport of spin-polarized electrons across nonmagnetic III-V semiconductor multiple barriers is considered theoretically. We have calculated the spin dependent transmission coeficient, for conducting electrons transversing lattice-matched In0. 53Ga0. 47As/GaAs0. 5Sb0: /In0. 53Ga0. 47As [...] / InP/In0. 53Ga0. 47As nanostructures with different numbers of asymmetric double barriers, as a function of electron energy and angle of incidence. Spin-orbit split resonances, due to the Rashba term, are observed. The envelope function approximation and the Kane k ·p model for the bulk are used. For an unpolarized incident beam of electrons, we also obtain the spin polarization of the transmitted beam. The formation of spin dependent minibands of energy with nonzero transmission is observed.

  5. On the recollision-free excitation of krypton during ultrafast multi-electron tunnel ionization

    CERN Document Server

    Bryan, W A; McKenna, J; English, E M L; Suresh, M; Wood, J; Srigengan, B; Turcu, I C E; Williams, I D; Newell, W R

    2006-01-01

    The probability of multiple ionization of krypton by 50 femtosecond circularly polarized laser pulses, independent of the optical focal geometry, has been obtained for the first time. The excellent agreement over the intensity range 10 TWcm-2 to 10 PWcm-2 with the recent predictions of A. S. Kornev et al [Phys. Rev. A v.68, art.043414 (2003)] provides the first experimental confirmation that non-recollisional electronic excitation can occur in strong field ionization. This is particularly true for higher stages of ionization, when the laser intensity exceeds 1 PWcm-2 as the energetic departure of the ionized electron(s) diabatically distorts the wavefunctions of the bound electrons. By scaling the probability of ionization by the focal volume, we discusses why this mechanism was not apparent in previous studies.

  6. Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes

    OpenAIRE

    Steele, G A; Gotz, G.; Kouwenhoven, L. P.

    2009-01-01

    Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies and research into new device applications. In particular, they have unique properties that make them attractive for studying the coherent properties of single electron spins. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers, but disorder has until now prevented tunable nanotube-based quantum-dot devices from reaching ...

  7. Resonant tunneling of interacting electrons in a one-dimensional wire

    OpenAIRE

    Nazarov, Yu V.; Glazman, L. I.

    2002-01-01

    We consider the conductance of a one-dimensional wire interrupted by a double-barrier structure allowing for a resonant level. Using the electron-electron interaction strength as a small parameter, we are able to build a non-perturbative analytical theory of the conductance valid in a broad region of temperatures and for a variety of the barrier parameters. We find that the conductance may have a non-monotonic crossover dependence on temperature, specific for a resonant tunn...

  8. Transport of electrons in the tunnel of an ion sensitive probe

    International Nuclear Information System (INIS)

    Ion sensitive probes serve to measure the ion temperature in magnetized plasma. Such a probe typically consists of a collector submerged inside a hollow tube, which is oriented perpendicularly to the magnetic field. The principle of the probe is based on geometrical shielding of the ion collector from plasma electrons. According to the basic theory, when the collector is retracted in the tube, electrons with their small Larmor radii should not be able to reach it and the collector becomes sensitive to ions. However, experimental results show that the electron shielding is in general inefficient, it only works in the case when the potential of the collector is the same as the potential of the inside surface of the tube. This problem is investigated using a full 3D particle-in-cell Cartesian code with a fast multigrid Poisson solver. We simulate the plasma behaviour in the vicinity of a model of the ion sensitive probe. A positive potential structure is formed at the entrance of the tube due to the space charge of ions that gyrate inside. This structure produces E x B drifts, which push electrons into the shielded space. A stream of electrons hitting the collector is observed for various potentials of the collector. Simulations revealed that electrons can penetrate inside the geometrical shadow in all studied cases; however, they do not reach the collector when the potential of the collector is equal to the potential of the tube..

  9. Tunneling and migration of the dumbbell defect in electron irradiated aluminum-zinc alloys

    International Nuclear Information System (INIS)

    Ultrasonic attenuation and velocity measurements have been made on irradiated Al-Zn alloys (Zn concentrations of .01%, .1%, and .5% atomic). They provide strong evidence for a tunneling relaxation of the predominant mixed dumbbell defect at low temperatures and for mixed dumbbell migration at the Stage II anneal temperature. The effect of an internal strain varying with the zinc concentration of the measured decrement and modulus change is striking. Evaluated in the framework of a six level system, this reveals the simultaneous action of resonance and non-classical relaxation processes. Using Fe as a probe atom, it is shown that mixed dumbbell dissociation is in an insignificant component of the annealing of this defect. The decrease of the annealing temperature at higher zinc concentrations provides evidence that the mixed dumbbell migrates as a unit during annealing. The energies associated with dumbbell migration and interstitial escape are derived. Further evidence for the migration mechanism is obtained from successive irradiation and annealing measurements on the Al-Zn .01% alloy, and from a comparison of these results with published radiation damage rate measurements of dilute Al-Zn alloys

  10. Electronic transport through EuO spin-filter tunnel junctions

    KAUST Repository

    Jutong, Nuttachai

    2012-11-12

    Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the ?1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

  11. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment.

    Science.gov (United States)

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M

    2015-03-21

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near room temperature. This expression also holds when a broad protein conformational distribution of D-A equilibrium distances dominates the spread of the D-A vibrational wavefunction. PMID:25796225

  12. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: Comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment

    Science.gov (United States)

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M.

    2015-03-01

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near room temperature. This expression also holds when a broad protein conformational distribution of D-A equilibrium distances dominates the spread of the D-A vibrational wavefunction.

  13. Experimental investigation of the possibilities of the optical tunnelling of electron from a metal surface induced by strong CO2 laser pulses

    International Nuclear Information System (INIS)

    According to the fundamental laws of the intense field QED, the general processes governing the laser-induced electron emission from atoms or solids traditionally may be interpreted as two complementary limiting interaction processes of the same phenomenon. The first is the multiphoton type process, when the electron interacts only with several well determined small number of photons (quantum limit), the second is the tunnelling type, when the number of the interacting photons is increasingly high (classical limit). While practically all research activity was concentrated both theoretically and experimentally to the multiphoton questions, less attention was paid to the tunnelling case, in spite of the fact that the early beginning of the intense field QED started with the pronunciation of this latter. After a short summarizing formulation of the topics, we describe several experiments performed by use at the Laval University for the study of the laser induced tunnelling. The surface photoeffect of gold proved to be a good experimental tool for these studies giving complementary results to the experiments carried out by use for the tunnel ionization of gas atoms. 36 references, 9 figures

  14. Controlling user access to electronic resources without password

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Fred Hewitt

    2015-06-16

    Described herein are devices and techniques for remotely controlling user access to a restricted computer resource. The process includes pre-determining an association of the restricted computer resource and computer-resource-proximal environmental information. Indicia of user-proximal environmental information are received from a user requesting access to the restricted computer resource. Received indicia of user-proximal environmental information are compared to associated computer-resource-proximal environmental information. User access to the restricted computer resource is selectively granted responsive to a favorable comparison in which the user-proximal environmental information is sufficiently similar to the computer-resource proximal environmental information. In at least some embodiments, the process further includes comparing user-supplied biometric measure and comparing it with a predetermined association of at least one biometric measure of an authorized user. Access to the restricted computer resource is granted in response to a favorable comparison.

  15. Electronic Resource Management 2.0: Using Web 2.0 Technologies as Cost-Effective Alternatives to an Electronic Resource Management System

    Science.gov (United States)

    Murray, Adam

    2008-01-01

    Designed to assist with the management of e-resources, electronic resource management (ERM) systems are time- and fund-consuming to purchase and maintain. Questions of system compatibility, data population, and workflow design/redesign can be difficult to answer; sometimes those answers are not what we'd prefer to hear. The two primary functions…

  16. Fano effect upon tunneling of a spin-polarized electron through a single magnetic impurity

    Science.gov (United States)

    Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.

    2013-01-01

    The calculations of transport characteristics of a single magnetic impurity showed that the presence of different effective channels for electron transmission results in the Fano effect. It was noticed that the external magnetic field and gate voltage allow controlling the conducting properties, which are governed by the configuration interaction between the states of the system.

  17. Efficient algorithm for current spectral density calculation in single-electron tunneling and hopping

    CERN Document Server

    Sverdlov, V A; Korotkov, A N; Sverdlov, Viktor A.; Kinkhabwala, Yusuf A.; Korotkov, Alexander N.

    2005-01-01

    This write-up describes an efficient numerical method for the Monte Carlo calculation of the spectral density of current in the multi-junction single-electron devices and hopping structures. In future we plan to expand this write-up into a full-size paper.

  18. Bridging the Two Cultures: A Collaborative Approach to Managing Electronic Resources.

    Science.gov (United States)

    Dupuis, John; Ryan, Patti

    2002-01-01

    Highlights an example of cross-discipline collaboration in an academic library and describes a collaborative approach to managing electronic resources that is used at York University (Canada). Explains a model in which a science librarian and a humanities/social science librarian work together to manage electronic resources. (Author/LRW)

  19. Using Google Calendar as an Email Alert System for Electronic Resource Renewals

    OpenAIRE

    Steven Shapiro

    2010-01-01

    This article describes an innovative and simple way for libraries to generate email reminders for the renewal and payment of electronic resources using Google Calendar. The advantages of using Google Calendar include cost (it’s free) and ease of use. Setting up an email alert system using Google Calendar enables librarians to track and manage their electronic resources more effectively.

  20. Using Google Calendar as an Email Alert System for Electronic Resource Renewals

    Directory of Open Access Journals (Sweden)

    Steven Shapiro

    2010-01-01

    Full Text Available This article describes an innovative and simple way for libraries to generate email reminders for the renewal and payment of electronic resources using Google Calendar. The advantages of using Google Calendar include cost (it’s free and ease of use. Setting up an email alert system using Google Calendar enables librarians to track and manage their electronic resources more effectively.

  1. Fabrication of Sub-Micron Size Al-AlOx-Al Tunnel Junction using Electron-Beam Lithography and Double-Angle Shadow Evaporation Technique

    International Nuclear Information System (INIS)

    We report our development of the fabrication process of sub-micron scale Al-AlOx-Al tunnel junction by using electron-beam lithography and double-angle shadow evaporation technique. We used double-layer resist to construct a suspended bridge structure, and double-angle electron-beam evaporation to form a sub-micron scale overlapped junction. We adopted an e-beam insensitive resist as a bottom sacrificing layer. Tunnel barrier was formed by oxidation of the bottom aluminum layer between the bottom and top electrode deposition, which was done in a separate load-lock chamber. The junction resistance is designed and controlled to be 50 ?to match the impedance of the transmission line. The junctions will be used in the broadband shot noise thermometry experiment, which will serve as a link between the electrical unit and the thermodynamic unit.

  2. Electronic resource management practical perspectives in a new technical services model

    CERN Document Server

    Elguindi, Anne

    2012-01-01

    A significant shift is taking place in libraries, with the purchase of e-resources accounting for the bulk of materials spending. Electronic Resource Management makes the case that technical services workflows need to make a corresponding shift toward e-centric models and highlights the increasing variety of e-formats that are forcing new developments in the field.Six chapters cover key topics, including: technical services models, both past and emerging; staffing and workflow in electronic resource management; implementation and transformation of electronic resource management systems; the ro

  3. Inelastic tunnel transport of electrons through an anisotropic magnetic structure in an external magnetic field

    Science.gov (United States)

    Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.

    2014-07-01

    Quantum transport of electrons through a magnetic impurity located in an external magnetic field and affected by a substrate is considered using the Keldysh diagram technique for the Fermi and Hubbard operators. It is shown that in a strongly nonequilibrium state induced by multiple reflections of electrons from the impurity, the current-voltage ( I-V) characteristic of the system contains segments with a negative conductivity. This effect can be controlled by varying the anisotropy parameter of the impurity center as well as the parameters of coupling between the magnetic impurity and metal contacts. The application of the magnetic field is accompanied by an increase in the number of Coulomb steps in the I-V curve of the impurity. The effect of appreciable magnetoresistance appears in this case. We demonstrate the possibility of switching between magnetic impurity states with different total spin projection values in the regime of asymmetric coupling of this impurity with the contacts.

  4. Single electron tunneling through high-Q single-wall carbon nanotube NEMS resonators

    OpenAIRE

    Huettel, A. K.; Meerwaldt, H. B.; Steele, G. A.; Poot, M.; Witkamp, B.; Kouwenhoven, L. P.; Zant, H. S. J.

    2010-01-01

    By first lithographically fabricating contact electrodes and then as last step growing carbon nanotubes with chemical vapour deposition across the ready-made chip, many potential contamination mechanisms for nanotube devices can be avoided. Combining this with pre-defined trenches on the chip, such that the nanotubes are freely suspended above the substrate, enables the formation of highly regular electronic systems. We show that, in addition, such suspended ultra-clean nano...

  5. Surge current and electron swarm tunnel tests of thermal blanket and ground strap materials

    Science.gov (United States)

    Hoffmaster, D. K.; Inouye, G. T.; Sellen, J. M., Jr.

    1977-01-01

    The results are described of a series of current conduction tests with a thermal control blanket to which grounding straps have been attached. The material and the ground strap attachment procedure are described. The current conduction tests consisted of a surge current examination of the ground strap and a dilute flow, energetic electron deposition and transport through the bulk of the insulating film of this thermal blanket material. Both of these test procedures were used previously with thermal control blanket materials.

  6. Tunnel probes for measurements of the electron and ion temperature in fusion plasmas.

    Czech Academy of Sciences Publication Activity Database

    Gunn, J. P.; Schrittwieser, R.; Balan, P.; Ionita, C.; Stöckel, Jan; Adámek, Ji?í; ?uran, Ivan; Hron, Martin; Pánek, Radomír; Ba?ina, O.; Hrach, R.; Vicher, M.; Van Oost, G.; Van Rompuy, T.; Martines, E.

    2004-01-01

    Ro?. 75, ?. 10 (2004), s. 4328-4330. ISSN 0034-6748. [Topical Conference on High-Temperature Plasma Diagnostics/15th./. San Diego, 19.04.2004-22.04.2004] R&D Projects: GA ?R GA202/03/0786 Institutional research plan: CEZ:AV0Z2043910 Keywords : Tokamak * electron temperature * ion temperature * plasma diagnostics Subject RIV: BG - Nuclear, Atomic and Molecular Phy sics, Colliders Impact factor: 1.226, year: 2004

  7. Electron tunneling in very low energy C sub 6 sub 0 -surface collisions Probing normal and tangential exit velocity effects

    CERN Document Server

    Bekkerman, A; Kolodney, E

    2002-01-01

    Normal and tangential exit velocity effects were studied for negative ion formation in collisions of very low energy (E sub 0 =10-40 eV) neutral C sub 6 sub 0 molecular beams with a conducting surface. The normal and tangential velocity components of the scattered C sub 6 sub 0 sup - were (1.3-5.6)x10 sup - sup 4 a.u. and (0.8-3.1)x10 sup - sup 4 a.u. correspondingly. The average vibrational energy per C sub 6 sub 0 molecule was kept nearly constant for all E sub 0 values. The C sub 6 sub 0 sup - yield was found to decrease exponentially with the inverse of the normal velocity component for both near normal and near grazing incidence angles. Practically the same slope, within experimental uncertainty, was extracted from the semilog yield plots showing that tangential velocity effects are negligible. The distance dependent electron tunneling rates from C sub 6 sub 0 sup - to the conducting surface were calculated and the results were used in order to derive a characteristic distance for ion formation.

  8. Interaction effects on the tunneling of electron-hole pairs in coupled quantum dots

    Science.gov (United States)

    Guerrero, Hector M.; Cocoletzi, Gregorio H.; Ulloa, Sergio E.

    2001-03-01

    The transit time of carriers is beginning to be an important parameter in the physical operation of semiconductor quantum dot `devices'. In the present work, we study the coherent propagation of electron-hole pairs in coupled self-assembled quantum dots in close proximity. These systems, achieved experimentally in a number of different geometries, have been recently implemented as a novel storage of optical information that may give rise to smart pixel technology in the near future [1]. Here, we apply an effective mass hamiltonian approach and solve numerically the time dependent Schroedinger equation of a system of photo-created electron-hole pairs in the dots. Our approach takes into account both Coulomb interactions and confinement effects. The time evolution is investigated in terms of the structural parameters for typical InAs-GaAs dots. Different initial conditions are considered, reflecting the basic processes that would take place in these experiments. We study the probabilities of finding the electron and hole in either the same or adjacent quantum dot, and study carefully the role of interactions in this behavior. [1] T. Lundstrom, W. Schoenfeld, H. Lee, and P. M. Petroff, Science 286, 2312 (1999).

  9. Tarsal Tunnel Syndrome

    Science.gov (United States)

    ... Tarsal Tunnel Syndrome Text Size Print Bookmark Tarsal Tunnel Syndrome What Is the Tarsal Tunnel? The tarsal tunnel is a narrow space that ... focus of tarsal tunnel syndrome. What Is Tarsal Tunnel Syndrome? Tarsal tunnel syndrome is a compression, or ...

  10. The Relevancy of Graduate Curriculum to Human Resource Professionals' Electronic Communication.

    Science.gov (United States)

    Hoell, Robert C.; Henry, Gordon O.

    2003-01-01

    Electronic communications of human resource professionals and the content of 23 university human resource management courses were categorized using the Human Resource Certification Institute's body of knowledge. Differences between proportion of topics discussed and topics covered in curricula suggest some topics are over- or undertaught.…

  11. Strategic Planning for Electronic Resources Management: A Case Study at Gustavus Adolphus College

    Science.gov (United States)

    Hulseberg, Anna; Monson, Sarah

    2009-01-01

    Electronic resources, the tools we use to manage them, and the needs and expectations of our users are constantly evolving; at the same time, the roles, responsibilities, and workflow of the library staff who manage e-resources are also in flux. Recognizing a need to be more intentional and proactive about how we manage e-resources, the…

  12. Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope

    OpenAIRE

    StorgardsStorgards, J.; Méndez Martín, Bianchi; Piqueras de Noriega, Javier; Storgards, M.; Dimroth, F.; Bett, A.W.

    2004-01-01

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) rising a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to t...

  13. Spin-flip induction of Fano resonance upon electron tunneling through atomic-scale spin structures

    Science.gov (United States)

    Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.

    2013-05-01

    The inclusion of inelastic spin-dependent electron scatterings by the potential profiles of a single magnetic impurity and a spin dimer is shown to induce resonance features due to the Fano effect in the transport characteristics of such atomic-scale spin structures. The spin-flip processes leading to a configuration interaction of the system's states play a fundamental role for the realization of Fano resonance and antiresonance. It has been established that applying an external magnetic field and a gate electric field allows the conductive properties of spin structures to be changed radically through the Fano resonance mechanism.

  14. Quantum Tunneling of an Acoustic Polaron in One-Dimensional Electron-Lattice System

    Science.gov (United States)

    Ono, Yoshiyuki; Ebinuma, Takashi; Ozawa, Toshiyuki

    More than two decades ago, Donovan and Wilson [1] found peculiar charge carriers with an anomalously high mobility in photo-conduction experiments on polydiacetylene which belongs to conjugated polymers and could be regarded as a quasi-one-dimensional system; for example, in the single crystal of polydiacetylene toluene sulphonate, one of typical polydiacetylene, the minimum distance between neighboring polymer chains is 0.75 nm [2] which is much larger than the bond length between carbon atoms (˜ 0.13 nm). The characteristics of the photo-excited charge carriers are summarized as follows; (1) they have a rather high mobility which is estimated to be no less than 20 m2/(sec·V), and (2) their drift velocity shows saturation at a value of the order of the sound velocity v s of the system in the applied electric field with the strength 102 to 106 V/m. For a possible explanation of this charge carrier, Wilson [3] proposed an acoustic polaron which is a composite of an electron near the conduction band bottom and lattice distortions induced by the presence of the electron and giving rise to an effective attractive potential confining the electron to a locally distorted lattice region. In fact, starting from Su, Schrieffer and Heeger's (SSH) model [4] which is one of the standard theoretical models for one-dimensional coupled electron-lattice systems, Wilson [3] could derive theoretically the following properties of an acoustic polaron within the continuum approximation which is justified in the weak coupling limit; (1) the polaron has a saturation velocity equal to the sound velocity of the system, (2) the extent of the polaron (referred to as "width" in the following) decreases with increasing velocity and tends to vanish as the velocity v approaches the saturation velocity (= the sound velocity, ), and (3) the energy of the moving polaron diverges as (v s -v)-3 when the polaron velocity v approaches v s . These properties of the acoustic polaron were confirmed later by numerical simulations [5] treating the SSH model as it is without assuming the weak coupling limit; details of these simulations will be explained in the following section.

  15. "Not" a One-Size-Fits-All Solution: Lessons Learned from Implementing an Electronic Resources Management System in Three Days

    Science.gov (United States)

    Pan, Denise

    2009-01-01

    Auraria Library purchased Innovative Interfaces, Inc.'s Millennium Electronic Resources Management (ERM) to manage data about acquisitions, licensing, troubleshooting, and usage statistics of electronic resources. After 3 days of implementation, the software vendor enabled resources records to display. As a result, the electronic resources team…

  16. Effect of quantum tunneling on single strand breaks in a modeled gas phase cytidine nucleotide induced by low energy electron: A theoretical approach

    Science.gov (United States)

    Bhaskaran, Renjith; Sarma, Manabendra

    2013-07-01

    Effect of quantum mechanical tunneling on single strand breaks induced by low energy electron (LEE) has been investigated in a modeled gas phase system, 2'-deoxycytidine-3'-monophosphate (3'-dCMPH). The potential energy curves for the sugar-phosphate C-O (3' C-O) bond cleavage have been generated using second order Møller-Plesset perturbation theory at the 6-31+G(d) accuracy level. Results from the electronic structure theory calculations in conjunction with our time dependent calculations for the 3' C-O bond rupture in 3'-dCMPH using local complex potential based time dependent wave packet approach show significant quantum tunneling of the 3' C-O bond from the bound vibrational states above 1 eV of the anionic potential energy curve. A comparison of the fragmentation profile with that of our earlier gas phase investigations based on Hartree-Fock and density functional theory - Becke, 3-parameter, Lee-Yang-Parr methods with 6-31+G(d) basis set is also provided. Further, inspection of the singly occupied molecular orbitals generated at different 3' C-O bond lengths clearly indicates the electron transfer from the low lying base-?* shape resonance state to the phosphate P = O ?* orbital of the DNA backbone during the strand breaks. The decisive step during LEE induced strand breaks follows via "charge induced dissociation" (CID) for the metastable anion formed below 1 eV, whereas quantum mechanical tunnel-ing is out-weighted the CID mechanism for the LEE above 1 eV.

  17. Tunneling Processes in Optically Excited Quantum Dots

    International Nuclear Information System (INIS)

    The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts: the electron and the hole parts, which are analytically obtained in the framework of the Keldysh formalism. The tunneling process is selective tunneling, which results in dark tunneling states. The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  18. Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments

    CERN Document Server

    Le Sueur, H

    2006-01-01

    The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating an STM in a dilution refrigerator we have designed a room temperature tunnel current amplifier having very small back-action on the tunnel contact and allowing to nearly reach the predicted energy resolution. This design is a modification of the standard op-amp based tip-biasing current-voltage converter which implements differential voltage sensing and whose back action on the tip voltage is only \\~2 $\\mu$V rms for a 14 MV/A transimpedance and 22 kHz bandwidth.

  19. Time-dependent exchange and tunneling: detection at the same place of two electrons emitted simultaneously from different sources

    OpenAIRE

    Marian, D.; Colomés, E.; Oriols, X.

    2014-01-01

    Two-particle scattering probabilities in tunneling scenarios with exchange interaction are analyzed with quasi-particle wave packets. Two initial one-particle wave packets (with opposite central momentums) are spatially localized at each side of a barrier. After impinging upon a tunneling barrier, each wave packet splits into transmitted and reflected components. When the initial two-particle anti-symmetrical state is defined as a Slater determinant any type of (normalizable...

  20. Scanning tunneling microscopy and spectroscopy studies on structural and electronic properties of thin films of Co oxides and oxide precursor states on Ag(001)

    Energy Technology Data Exchange (ETDEWEB)

    Shantyr, R.; Hagendorf, Ch.; Neddermeyer, H

    2004-10-01

    The main aim of this work is the electronic characterization of various Co oxide and precursor states on Ag(001), which grow during reactive deposition by evaporating Co from a Knudsen cell in an O{sub 2} atmosphere. We have identified double-layer CoO(001) and monolayer and double-layer CoO(111), which show distinct differences in the I/U and (dI/dU)/(I/U) characteristics of scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). CoO(001) and, to some extent, also double-layer CoO(111) exhibit oxidic behavior. For CoO(001), the oxidic character is particularly recognized in the contrast dependence as a function of sample bias U.

  1. ODLIS : Online Dictionary for Library and Information Science [electronic resource].

    International Nuclear Information System (INIS)

    A hypertext reference resource for library and information science professionals, university students and faculty, and users of all types of libraries. Includes not only the terminology of the various specializations within library science and information studies but also the vocabulary of publishing, printing, binding, the book trade, graphic arts, book history, literature, bibliography, telecommunications, and computer science.

  2. A comparative analysis of the use of electronic resources by undergraduate students at two Kenyan universities

    OpenAIRE

    Ingutia-oyieke, Lilian; Dick, Archie L.

    2010-01-01

    This article compares the information and communication technology (ICT) infrastructures, the levels of access, and the electronic resources usage patterns at two academic libraries in Kenya. The focus is on the use by undergraduate students at the private University of Eastern Africa, Baraton (UEAB) and the public Kenyatta University (KU) of electronic resources to support formal and informal learning. The article also briefly explores the perceptions of library managers with regard to teach...

  3. Use and Search Pattern of Electronic Resources in Five Autonomous Engineering Colleges (Bengaluru

    Directory of Open Access Journals (Sweden)

    Mallinath Kumbar

    2012-12-01

    Full Text Available Purpose: This study evaluates the use of electronic resources among the faculty in five autonomous Engineering Colleges in Bengaluru. It evaluates the purpose,benefits, preference of web browsers, search engines, file formats, problem faced,and search patterns as the key parameters. It highlights some problems,constraints and forward suggestions for better use of electronic resources.Methodology/Approach: The structured questionnaire is used for data collection besides personal interview and observation to add clarity.Findings: The study assesses the faculty awareness and use of electronic resources in their academic and research needs. Besides, familiarity about search patterns for effective retrieval.Research Limitations: The study is limited to the faculty of the Autonomous Engineering Colleges affiliated to Visvesvaraya Technological University (VTU in Bengaluru Region of Karnataka State, India.Keywords: e-resources; search pattern; e-resource use; Autonomous Engineering Colleges.Paper Type: Survey cum Research

  4. Using Electronic Repositories as a Student Resource for MSE Applications

    Science.gov (United States)

    Blicblau, Aaron

    In the majority of engineering disciplines, MSE provides resources and applications with many other areas of engineering, e.g., design, structures, mechanics, and manufacturing. For the students to transfer and implement their MSE knowledge, they must have easy access to all their information. The eportfolio is a repository of the students entire academic MSE content and provides a wealth of knowledge applicable to all engineering disciplines. This repository combines not only lecture and textbook material, but also every assignment (in assessed format), all quizzes (with answers) laboratory activities (in audiovisual format), student oral presentations (podcast), and lectures in asynchronous format. This allows all of the data and information accumulated by students throughout their varying MSE course collected in one place, and is able to act as a quick resource and information kit for future use as the eportfolio is quickly accessed. Student and graduate responses have been positive especially for those in the workforce who require immediate and correct information.

  5. Tunnel Through!

    Science.gov (United States)

    Integrated Teaching and Learning Program,

    Students apply their knowledge about mountains and rocks to transportation engineering, with the task of developing a model mountain tunnel that simulates the principles behind real-life engineering design. Student teams design and create model tunnels through a clay mountain, working within design constraints and testing for success; the tunnels must meet specific design requirements and withstand a certain load.

  6. ?????????????????????? A Study of Demands Analysis and Marketing Strategy of Electronic Resources in University Library

    Directory of Open Access Journals (Sweden)

    Huang-Yu Liu

    2008-03-01

    Full Text Available ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????/??????????????????????????????????????????????????The emergence of electronic resources has made new breakthrough in knowledge carriers because of their ease of use, instant availability, and the characteristic of no time and space constraints. For public libraries to achieve maximum efficiency in its electronic resources, it is necessary to seek the most effective marketing strategies. Therefore, the marketing concept of the electronic resources should be reader oriented, such as respecting and understanding library user’s information needs. Libraries also need to utilize various media and techniques to market the electronic resources, so that more comprehensive services and experiences can be provided to readers. The purpose of this study is to investigate library user’s needs and promotion strategies of electronic resources in order to identify the most effective ways of marketing. This study focuses on the students of the four colleges (College of Business, College of Tourism, College of Information, and College of Humanities and Social Science in Kainan University as subjects in the survey questionnaire. It uses the Gap Analysis Model as the main analytical tool to examine cases in which readers/ students show real demands to electronic resources. The study concludes with promotion and marketing strategies with regards to service offerings for the university libraries.

  7. Resource note: Theoretical atomic-electron binding energies

    International Nuclear Information System (INIS)

    An annotated bibliography of calculations of electron binding energies of neutral atoms is presented. The subject is summarized in a brief introduction. Published calculations are tabulated; entries are characterized according to range of atomic numbers; type of atomic model; nuclear charge distribution; and inclusion of relaxation, Breit interaction, and quantum-electrodynamic effects. The table is supplemented with a chronological list of selected papers on atomic structure calculations and with a list of references to some useful computer programs. copyright 1987 Academic Press, Inc

  8. Managing Selection for Electronic Resources: Kent State University Develops a New System to Automate Selection

    Science.gov (United States)

    Downey, Kay

    2012-01-01

    Kent State University has developed a centralized system that manages the communication and work related to the review and selection of commercially available electronic resources. It is an automated system that tracks the review process, provides selectors with price and trial information, and compiles reviewers' feedback about the resource. It…

  9. Electronic resources and institutional repositories in informal scholarly communication and publishing

    OpenAIRE

    Galina Russell, I.

    2009-01-01

    The aim of institutional repositories is to aid the management and dissemination of the increasingly copious amount of scholarly electronic resources produced by academics. To date most research has focused on the impact for formal scholarly publishing. The purpose of this exploratory study is to discover the impact of IRs on the visibility and use of digital resources with particular focus on resources outside the formal publishing framework. An online survey and interviews wi...

  10. Characteristics of Tunneling Nitride Grown by Electron Cyclotron Resonance Nitrogen-Plasma Nitridation and Its Application to Low-Voltage Electrical Erasable-Programmable Read-Only Memory

    Science.gov (United States)

    Min, Kyeong-Sik; Chung, Jin-Yong; Lee, Kwyro

    2001-04-01

    Characteristics of a tunneling-nitride insulator grown by low-temperature electron cyclotron resonance (ECR) nitrogen-plasma nitridation are presented. The ECR nitridation shows a very high growth rate at lower temperatures and the thickness is proportional to the growth time. For example, we obtain a thickness of 16 [nm] and a refractive index of 1.75 after the nitridation time of 80 [min] at 400°C. The barrier heights measured from the Fowler-Nordheim (F-N) tunneling current are 2.3 [eV] and 1.4 [eV] in the inversion and the accumulation modes, respectively. These lower heights allow us much faster programming and erasing times of an electrical erasable-programmable read-only memory (EEPROM) with the ECR nitride than those of the conventional EEPROM with the thermal oxide. A double-gate EEPROM with an ECR-nitride tunneling insulator was fabricated. Surprisingly, it does not show any threshold voltage (VTH) degradation even after 100,000 cycles of programming and erasing.

  11. Simulation of stress-induced leakage current in silicon dioxides: A modified trap-assisted tunneling model considering Gaussian-distributed traps and electron energy loss

    Science.gov (United States)

    Chang, Wai Jyh; Houng, Mau Phon; Wang, Yeong Her

    2001-06-01

    In this article, a modified generalized trap-assisted tunneling model (GTAT) is proposed to explain the excessive currents occurring at low electric fields during stressing (stress-induced leakage current, SILC). Parameters such as trap energy level, Gaussian-distributed traps, and energy loss (when electrons tunnel through an oxide) are all included in this model. The trap energy levels relative to the effective Fowler-Nordheim tunneling barriers (?B) are classified into either shallow traps or deep traps. Quantitative analyses of the effects of oxide thickness, trap energy levels, trap concentrations, and energy losses on SILC are performed. Examples relating to the SILC of thermal oxides are shown to validate the suitability of our GTAT model. Good agreement between experimental data and the simulated current-voltage curves using this model is obtained for various SILC phenomena. The extracted trap energy levels exist between 1.5 and 2.0 eV for shallow traps and at 3.2 eV for deep traps, while trap concentrations are in the range of 1018-1020 cm-3 depending on various stress conditions. The energy level of induced traps and trap concentration can be easily derived from this model without the need for other complicated measurements. This model is demonstrated to be an accurate and reliable SILC model for investigating ultrathin gate oxide devices in integrated circuits of future generations.

  12. Simulation of stress-induced leakage current in silicon dioxides: A modified trap-assisted tunneling model considering Gaussian-distributed traps and electron energy loss

    International Nuclear Information System (INIS)

    In this article, a modified generalized trap-assisted tunneling model (GTAT) is proposed to explain the excessive currents occurring at low electric fields during stressing (stress-induced leakage current, SILC). Parameters such as trap energy level, Gaussian-distributed traps, and energy loss (when electrons tunnel through an oxide) are all included in this model. The trap energy levels relative to the effective Fowler - Nordheim tunneling barriers (?B) are classified into either shallow traps or deep traps. Quantitative analyses of the effects of oxide thickness, trap energy levels, trap concentrations, and energy losses on SILC are performed. Examples relating to the SILC of thermal oxides are shown to validate the suitability of our GTAT model. Good agreement between experimental data and the simulated current - voltage curves using this model is obtained for various SILC phenomena. The extracted trap energy levels exist between 1.5 and 2.0 eV for shallow traps and at 3.2 eV for deep traps, while trap concentrations are in the range of 1018 - 1020cm-3 depending on various stress conditions. The energy level of induced traps and trap concentration can be easily derived from this model without the need for other complicated measurements. This model is demonstrated to be an accurate and reliable SILC model for investigating ultrathin gate oxide devices in integrated circuits of future generations. [copyright] 2001 Americanre generations. [copyright] 2001 American Institute of Physics

  13. Influence of ablated and tunneled electrons on quasi-phase-matched high-order-harmonic generation in laser-produced plasma

    Science.gov (United States)

    Ganeev, Rashid A.; To?a, Valer; Kovács, Katalin; Suzuki, Masayuki; Yoneya, Shin; Kuroda, Hiroto

    2015-04-01

    Studies of the quasi-phase-matched harmonics generated in spatially modulated silver plasma are presented. We analyze the influence of the driving and heating pulse energies on the enhancement and spectral tuning of the quasi-phase-matched harmonics and show the tuning of those enhanced groups of harmonics by tilting the multislit mask placed in front of the ablated targets. Calculations performed in the laser-produced plasmas demonstrate the joint influence of the electrons that appeared during target ablation and tunnel ionization on the tuning of the quasi-phase-matching conditions in the plasmas.

  14. Influence of Rashba spin-orbit interaction on the transmission and the dwell time of the electron tunneling through a multiple quantum well structure

    International Nuclear Information System (INIS)

    In this paper we propose a model for computing the transmission coefficient and the dwell time of the electron tunneling through a multiple quantum well structure with Rashba spin-orbit interaction and with an external and constant electric field, using the transfer matrix formalism with piecewise constant potentials. The results indicate a difference between the transmission coefficients and the dwell times for spin-up and spin-down orientations. This difference can be modified by varying the electric field and the number of the barriers and wells, this opening the way to create a spin filtering in the time domain

  15. Programmable ferroelectric tunnel memristor

    OpenAIRE

    AndyQuindeau

    2014-01-01

    We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8])O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us...

  16. Semiclassical description of resonant tunneling

    International Nuclear Information System (INIS)

    A semiclassical formula is calculated for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The tunneling current is measured at the second interface of this well and the calculations idealized an experimental situation where a strong magnetic field tilted with respect to an electric field was used. It is shown that the contribution to the tunneling current, due to trajectories which begin at the first interface and end on the second, is dominant for periodic orbits which hit both walls of the quantum well. (author)

  17. The National Site Licensing of Electronic Resources: An Institutional Perspective

    Directory of Open Access Journals (Sweden)

    Xiaohua Zhu

    2011-06-01

    Full Text Available While academic libraries in most countries are struggling to negotiate with publishers and vendors individually or collaboratively via consortia, a few countries have experimented with a different model, national site licensing (NSL. Because NSL often involves government and large-scale collaboration, it has the potential to solve many problems in the complex licensing world. However, not many nations have adopted it. This study uses historical research approach and the comparative case study research method to explore the seemingly low level of adoption. The cases include the Canadian National Site Licensing Project (CNSLP, the United Kingdom’s National Electronic Site Licensing Initiative (NESLI, and the United States, which has not adopted NSL. The theoretical framework guiding the research design and data collection is W. Richard Scott’s institutional theory, which utilizes three supporting pillars—regulative, normative, and cultural-cognitive—to analyze institutional processes. In this study, the regulative pillar and the normative pillar of NSL adoption— an institutional construction and change—are examined. Data were collected from monographs, research articles, government documents, and relevant websites. Based on the analysis of these cases, a preliminary model is proposed for the adoption of NSL. The factors that support a country’s adoption of NSL include the need for new institutions, a centralized educational policy-making system and funding system, supportive political trends, and the tradition of cooperation. The factors that may prevent a country from adopting NSL include decentralized educational policy and funding, diversity and the large number of institutions, the concern for the “Big Deal,” and the concern for monopoly.

  18. Electroresistance effects in ferroelectric tunnel barriers

    OpenAIRE

    Pantel, Daniel; Alexe, Marin

    2010-01-01

    Electron transport through fully depleted ferroelectric tunnel barriers sandwiched between two metal electrodes and its dependence on ferroelectric polarization direction are investigated. The model assumes a polarization direction dependent ferroelectric barrier. The transport mechanisms, including direct tunneling, Fowler-Nordheim tunneling and thermionic injection, are considered in the calculation of the electroresistance as a function of ferroelectric barrier properties...

  19. Quantum size effects on spin-tunneling time in a magnetic resonant tunneling diode

    OpenAIRE

    Saffarzadeh, Alireza; Daqiq, Reza

    2009-01-01

    We study theoretically the quantum size effects of a magnetic resonant tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on the spin-tunneling time and the spin polarization of the electrons. The results show that the spin-tunneling times may oscillate and a great difference between the tunneling time of the electrons with opposite spin directions can be obtained depending on the system parameters. We also study the effect of structural asymmetry whi...

  20. Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage in the case of fully adiabatic electron transition

    International Nuclear Information System (INIS)

    Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage and on the width at half maximum of the current-overvoltage curve is studied. A number of the approximate expressions for the density of states, the tunnel current and the width are obtained in the fully adiabatic limit for different particular cases. It is shown that at small values of the coupling of the electronic levels of the electrodes with the valence orbital of the redox molecule and the small values of the bias voltage two regions of the reorganization Gibbs energy exist with different dependence of the width on the reorganization Gibbs energy. The results of calculations of the density of states, the tunnel current and the width are presented and used for the interpretation of the experimental data [N.G. Tao, Phys. Rev. Lett. 76 (1996) 4066, I. Visoly-Fisher, K. Daie, Y. Terazono, C. Herrero, F. Fungo, L. Otero, E. Durantini, J.J. Silber, L. Sereno, D. Gust, T.A. Moore, A.L. Moore, S.M. Lindsay, PNAS 103 (2006) 8686

  1. Spin Polarized Tunneling at Finite Bias

    Science.gov (United States)

    Valenzuela, S. O.; Monsma, D. J.; Marcus, C. M.; Narayanamurti, V.; Tinkham, M.

    2005-05-01

    A mesoscopic spin valve is used to determine the dynamic spin polarization of electrons tunneling out of and into ferromagnetic (FM) transition metals at finite voltages. The dynamic polarization of electrons tunneling out of the FM slowly decreases with increasing bias but drops faster and even inverts with voltage when electrons tunnel into it. A free-electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the matching of the electron wave function inside and outside the tunnel barrier.

  2. The effect of interface phonons on operating electron states in three-barrier resonant tunneling structure as an active region of quantum cascade detector

    Directory of Open Access Journals (Sweden)

    M.V. Tkach

    2014-06-01

    Full Text Available The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/AlxGa1-xAs which is an active region of quantum cascade detector. It is established that independently of the temperature, the energy of quantum transition during the process of electromagnetic field absorption is a nonlinear weakly varying function of the position of the inner barrier with respect to the outer barriers of the structure.

  3. The LEP tunnel

    CERN Multimedia

    Patrice Loiez

    1991-01-01

    The LEP collider, which ran from 1989 to 2000. Electrons and positrons were accelerated through these magnets until they were travelling at almost the speed of light before colliding in the centre of one of the four detectors. The huge circumference of the ring means that the curvature is very small and so the tunnel looks rather straight.

  4. Disseminating Context-Specific Access to Online Knowledge Resources within Electronic Health Record Systems

    OpenAIRE

    Fiol, Guilherme Del; Curtis, Clayton; Cimino, James J.; Iskander, Andrew; Kalluri, Aditya S. D.; Jing, Xia; Hulse, Nathan C.; Long, Jie; Overby, Casey L.; Schardt, Connie; Douglas, David M.

    2013-01-01

    Clinicians’ patient care information needs are frequent and largely unmet. Online knowledge resources are available that can help clinicians meet these information needs. Yet, significant barriers limit the use of these resources within the clinical workflow. Infobuttons are clinical decision support tools that use the clinical context (e.g., institution, user, patient) within electronic health record (EHR) systems to anticipate clinicians’ questions and provide automated links to relevan...

  5. Tombs, tunnels, and terraces a cultural resources survey of a former ammunition supply point in Okinawa, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Verhaaren, B. T.; Levenson, J. B.; Komine, G.

    2000-02-09

    U.S. forces serving at military bases on foreign soil are obligated to act as good stewards of the cultural and natural resources under their control. However, cultural resources management presents special challenges at U.S. bases in other countries where cultural properties laws differ in emphasis and detail from those in the United States and issues of land ownership and occupancy are not always clear. Where status of forces agreements (SOFAs) exist, environmental governing standards bridge the gap between U.S. and host nation cultural priorities. In Japan, the Department of Defense Japan Environmental Governing Standards (JEGS) fill this function. Under Criteria 12-4.2 and 12-4.3 of the JEGS, U.S. Forces Japan commit themselves to inventory and protect cultural properties found on the lands they control or use. Cultural properties include archaeological sites, tombs, historic buildings, and shrines. Natural monuments, such as landscape features or plant and animal species, may also be designated as cultural properties. As part of this commitment, in February 1999 a cultural resources inventory was conducted in Area 1, part of Kadena Air Base (AB), Okinawa, Japan. Area 1, the former U.S. army Ammunition Supply Point 1, is currently used primarily for training exercises and recreational paint ball.

  6. Scanning Tunneling Microscopy

    Science.gov (United States)

    The Concord Consortium

    2011-12-11

    Use a virtual scanning tunneling microscope (STM) to observe electron behavior in an atomic-scale world. Walk through the principles of this technology step-by-step. First learn how the STM works. Then try it yourself! Use a virtual STM to manipulate individual atoms by scanning for, picking up, and moving electrons. Finally, explore the advantages and disadvantages of the two modes of an STM: the constant-height mode and the constant-current mode.

  7. The Acquisition and Management of Electronic Resources: Can Use Justify Cost?

    Science.gov (United States)

    Koehn, Shona L.; Hawamdeh, Suliman

    2010-01-01

    As library collections increasingly become digital, libraries are faced with many challenges regarding the acquisition and management of electronic resources. Some of these challenges include copyright and fair use, the first-sale doctrine, licensing versus ownership, digital preservation, long-term archiving, and, most important, the issue of…

  8. Electron-tunneling study of superconductors doped with magnetic atoms and nonmagnetic resonant-state atoms: indium-chromium, zinc-manganese, and aluminum-manganese

    International Nuclear Information System (INIS)

    We have used electron-tunneling measurements to determine the density of states of quench-condensed thin films of In-Cr, Zn-Mn, and Al-Mn, and of annealed thin films of Zn-Mn. The results on In-Cr and Zn-Mn were compared with Shiba's theory for magentic atoms in superconductors. We observed the localized band of states predicted to form in the energy gap of such alloys, though the observed band was broader than that predicted. The annealed samples of Zn-Mn showed a narrower band than did the quench-condensed samples. Reasonable agreement with Shiba's theory was found if s, p, and d wave scattering were included. The results on Al-Mn were compared with Salomaa and Nieminen's theory for nonmagnetic resonant-state atoms in superconductors. The predicted band of states was not observed. Our measurements indicate that Mn in quench-condensed Al is nonmagnetic. Any resonant states which do exist in the superconducting alloy are too broad to be seen in our tunneling measurement

  9. Superconducting electron tunneling as detection method for low frequency resonant vibration modes of interstitials in fcc lead

    International Nuclear Information System (INIS)

    The influence of crystal defects on the phonon spectra was studied for fcc lead using superconducting tunneling spectroscopy. The theory predicts low frequency modes for the vibrational states of interstitials in (100) dumbbell configuration. Low temperature irradiation of superconducting point contacts with fast ions (point contact thickness small compared to the average ion range) showed radiation-induced structures in the low-energy part of the Eliashberg function for lead. These resonant modes are reduced by annealing at 18.5 K; they are attributed to small interstitial clusters. The radiation-induced structures are completely removed by room temperature annealing. (orig.)

  10. Semisimple tunnels

    OpenAIRE

    Cho, Sangbum; McCullough, Darryl

    2010-01-01

    A knot in the 3-sphere in genus-1 1-bridge position (called a (1,1)-position) can be described by an element of the braid group of two points in the torus. Our main results tell how to translate between a braid group element and the sequence of slope invariants of the upper and lower tunnels of the (1,1)-position. After using them to verify previous calculations of the slope invariants for all tunnels of 2-bridge knots and (1,1)-tunnels of torus knots, we obtain characteriza...

  11. Resonant Tunneling Spin Pump

    Science.gov (United States)

    Ting, David Z.

    2007-01-01

    The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling.

  12. Local electronic transport in La0.7Sr0.3MnO3 thin films studied by scanning tunneling potentiometry

    International Nuclear Information System (INIS)

    We have used a scanning tunneling microscope in potentiometry mode to investigate the local electric potential distribution in current carrying epitaxial La0.7Sr0.3MnO3 thin films, with magnetotransport properties similar to the ones of single crystals. Scans imaging simultaneously the surface topography and the potential distribution have been obtained with an unprecedented resolution. In textured La0.7Sr0.3MnO3/MgO, sharp potential steps coincide with some of the grain boundaries, whereas other grains are electrically well connected. The precise nature of the local electronic transport, the percolation of the current through the grain network, and the existence of phase separated insulating domains are then discussed

  13. Inelastic tunneling through mesoscopic structures

    CERN Document Server

    Haule, K

    1999-01-01

    Our objective is to study resonant tunneling of an electron in the presence of inelastic scattering by optical phonons. Using a recently developed technique, based on exact mapping of a many-body problem onto a one-body problem, we compute transmission through a single site at finite temperatures. We also compute current through a single site at finite temperatures and an arbitrary strength of the potential drop over the tunneling region. Transmission vs. incident electron energy at finite temperatures displays additional peaks due to phonon absorption processes. Current at a voltage bias smaller than the phonon frequency is dominated by elastic processes. We apply the method to an electron tunneling through the Aharonov-Bohm ring coupled to optical phonons. Elastic part of electron-phonon scattering does not affect the phase of the electron. Dephasing occurs only through inelastic processes.

  14. Stability Tunnel

    Science.gov (United States)

    1943-01-01

    Engineers operate the controls of the Stability Tunnel: Plans for a new tunnel to study stability problems began in the late thirties. The Stability Tunnel was authorized in 1939 and began operations in June 1941. The installation was completed in December that year with the completion of a new 10,000 Horsepower Diesel-electric generating plant. It was a single return, closed jet tunnel with a 6-foot square test section. The tunnel was disassembled and shipped to Virginia Polytechnic Institute and State University in 1958. The tunnel had two separate test sections: one for curved flow, the other for rolling flow. 'The facility...simulates the motion of the aircraft in curved or rolling flight. This is done by actually curving or rolling the airstream as it passes over the model and at the same time providing the proper velocity distribution.' (From AIAA-80-0309) >From Alan Pope, Wind-Tunnel Testing: 'The only tunnel directly designed for dynamic stability work is located at the Langley Field branch of the NACA. Its most vital feature is its ability to subject the models to curving air streams that simulate those actually encountered when an airplane rolls, pitches, or yaws. the rotating airstream for simulating roll is produced by a motor-driven paddle just ahead of the test section. Curved air of properly varying velocity for simulating pitch and yaw is produced by a combination of a curved test section and velocity screens. The proper use of this apparatus makes possible the determination of the stability derivatives.' (pp. 13-14)

  15. Atomic Layer Deposition of Tunnel Barriers for Superconducting Tunnel Junctions

    Science.gov (United States)

    Moyerman, Stephanie M.; Feng, Guangyuan; Krayer, Lisa; Stebor, Nathan; Keating, Brian G.

    2014-08-01

    We demonstrate a technique for creating high quality, large area tunnel junction barriers for normal-insulating-superconducting or superconducting-insulating-superconducting tunnel junctions. We use atomic layer deposition and an aluminum wetting layer to form a nanometer scale insulating barrier on gold films. Electronic transport measurements confirm that single-particle electron tunneling is the dominant transport mechanism, and the measured current-voltage curves demonstrate the viability of using these devices as self-calibrated, low temperature thermometers with a wide range of tunable parameters. This work represents a promising first step for superconducting technologies with deposited tunnel junction barriers. The potential for fabricating high performance junction refrigerators is also highlighted.

  16. Quantum Tunnelling to the Origin and Evolution of Life

    OpenAIRE

    Trixler, Frank

    2013-01-01

    Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating ...

  17. Signatures of electron-magnon interaction in charge and spin currents through magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach

    Science.gov (United States)

    Mahfouzi, Farzad; Nikoli?, Branislav K.

    2014-07-01

    We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the self-consistent perturbative expansion for the electron and magnon self-energies in the nonequilibrium Green function formalism applied to a coupled electron-magnon (e-m) system driven out of equilibrium by the applied finite bias voltage. Our scheme operates with the electronic and magnonic GFs and the corresponding self-energies viewed as matrices in the Keldysh space, rather than conventionally extracting their retarded and lesser components, which greatly simplifies translation of diagrams into compact mathematical expressions and their computational implementation. This is employed to understand the effect of inelastic e-m scattering on charge and spin current vs bias voltage Vb in F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs), which are modeled on a quasi-one-dimensional (quasi-1D) tight-binding lattice for the electronic subsystem and quasi-1D Heisenberg model for the magnonic subsystem. For this purpose, we evaluate the Fock diagram for the electronic self-energy and the electron-hole polarization bubble diagram for the magnonic self-energy. The respective electronic and magnonic GF lines within these diagrams are the fully interacting ones, thereby requiring to solve the ensuing coupled system of nonlinear integral equations self-consistently. Despite using the quasi-1D model and treating e-m interaction in many-body fashion only within a small active region consisting of few lattice sites around the F/I interface, our analysis captures essential features of the so-called zero-bias anomaly observed [V. Drewello, J. Schmalhorst, A. Thomas, and G. Reiss, Phys. Rev. B 77, 014440 (2008), 10.1103/PhysRevB.77.014440] in both MgO- and AlOx-based realistic 3D MTJs where the second derivative d2I /dVb2 (i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp peaks of opposite sign on either side Vb=0. We show that this is closely related to a substantially modified magnonic density of states (DOS) after the e-m interaction is turned on—the magnonic bandwidth over which DOS is nonzero becomes broadened, thereby making e-m scattering at arbitrary small bias voltage possible, while DOS also acquires peaks (on the top of a continuous background) signifying the formation of quasibound states of magnons dressed by the cloud of electron-hole pair excitations. We also demonstrate that the sum of electronic spin currents in all of the semi-infinite leads attached to the active region quantifies the loss of spin angular momentum carried away from the active region by the magnonic spin current.

  18. Tunneling conductance in gapped graphene-based normal metal-insulator-superconductor junctions: Case of massive Dirac electrons

    Science.gov (United States)

    Goudarzi, H.; Sedghi, H.; Khezerlou, M.; Mabhouti, Kh.

    2010-12-01

    We study the quantum transport property in a gapped graphene-based normal metal-insulator-superconductor junctions ( NG/ IG/ SG), in the limit of a thin barrier. The charged fermions in NG/ IG/ SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance’s in terms of some different electrostatic superconductor, U0 and barrier, V0 potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG ( EFN and EFN + U0, respectively), energy gap in graphene 2mvF2 and superconducting order parameter, ?, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take |EFN-mvF2|?0, it becomes as a step function of V0. This behavior of charge transportation can be considered as a nano switch.

  19. Tunneling conductance in gapped graphene-based normal metal-insulator-superconductor junctions: Case of massive Dirac electrons

    International Nuclear Information System (INIS)

    We study the quantum transport property in a gapped graphene-based normal metal-insulator-superconductor junctions (NG/IG/SG), in the limit of a thin barrier. The charged fermions in NG/IG/SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance's in terms of some different electrostatic superconductor, U0 and barrier, V0 potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG (EFN and EFN + U0, respectively), energy gap in graphene (2mvF2) and superconducting order parameter, ?, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take |EFN-mvF2|?0, it becomes as a step function of V0. This behavior of charge transportation can be considered as a nano switch.

  20. Tunnel recombinations in yttrium orthophosphate

    International Nuclear Information System (INIS)

    The tunnel luminescence induced by recombination of radiative centres is investigated in synthetic crystals of YPO4. Its spectrum, kinetics, effects of accumulation and connection with thermostimulated processes are studied in the temperature range from 80 to 220 K. It is shown that tunnel recombinations occur only in the genetically associated electron-hole centres. The paramagnetic centres (Zr3+, O-, SiO43-, Eu2+, ASO44-) are interpreted; their thermal stability and connection with the luminescence are investigated

  1. Tunneling spin-galvanic effect

    CERN Document Server

    Tarasenko, S A; Yassievich, I N

    2004-01-01

    It has been shown that tunneling of spin-polarized electrons through a semiconductor barrier is accompanied by generation of an electric current in the plane of the interfaces. The direction of this interface current is determined by the spin orientation of the electrons, in particular the current changes its direction if the spin orientation changes the sign. Microscopic origin of such a 'tunneling spin-galvanic' effect is the spin-orbit coupling-induced dependence of the barrier transparency on the spin orientation and the wavevector of electrons.

  2. Opening a Can of wERMS: Texas A&M University's Experiences in Implementing Two Electronic Resource Management Systems

    Science.gov (United States)

    Hartnett, Eric; Price, Apryl; Smith, Jane; Barrett, Michael

    2010-01-01

    Over the past few years, Texas A&M University (TAMU) has searched for a way to administer its electronic subscriptions as well as the electronic subscriptions shared among the TAMU System. In this article, we address our attempts to implement an effective electronic resource management system (ERMS), both for subscriptions on the main campus and…

  3. Programmable ferroelectric tunnel memristor

    Science.gov (United States)

    Quindeau, Andy; Hesse, Dietrich; Alexe, Marin

    2014-02-01

    We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8])O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

  4. Programmable ferroelectric tunnel memristor

    Directory of Open Access Journals (Sweden)

    AndyQuindeau

    2014-02-01

    Full Text Available We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8]O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

  5. Los recursos educativos electrónicos: perspectivas y herramientas de evaluación / Electronic educational resources: perspectives and evaluation tools

    Scientific Electronic Library Online (English)

    Maria, Pinto; Carmen, Gomez-Camarero; Andrés, Fernández-Ramos.

    2012-09-01

    Full Text Available Los recursos electrónicos con fines educativos están cada vez más presentes en los procesos de enseñanza-aprendizaje actuales, y por tanto, en las colecciones digitales de las bibliotecas. Ante su proliferación y heterogeneidad cada vez mayor se ha planteado como una necesidad para la comunidad univ [...] ersitaria definirlos y establecer un conjunto de criterios claros y relevantes de evaluación que permitan determinar la calidad de los mismos. En este trabajo se analizan las principales definiciones sobre recursos educativos electrónicos de cara a su acotación, se revisan las diferentes perspectivas para la evaluación de su calidad a través de la literatura científica, y se revisan las principales herramientas utilizadas para valorarlos. Finalmente, se presenta EVALUAREED, un instrumento diseñado para analizar y medir la calidad de los mismos, enfocado para ser utilizado por la comunidad universitaria, incluidas las bibliotecas. Abstract in english Electronic resources for education are increasingly present in the teaching-learning processes and in the digital library collections. Because of the proliferation and variety of educational resources, the educational community needs to define and establish a set of clear and relevant assessment to [...] determine their quality. This paper reviews the main definitions of electronic educational resources as well as different perspectives to the assessment of their quality through the scientific literature, and the main tools used to value them. Finally, it describes EVALUAREED, an instrument designed to analyze and measure the quality of these resources used by universitary community included the libraries.

  6. The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods

    CERN Document Server

    Krive, I V; Shekhter, R I; Jonson, M; Utko, P; Nygård, J

    2007-01-01

    The influence of fullerene molecules trapped inside a single-wall carbon nanotube on resonant electron transport at low temperature is discussed. Strong peak to peak fluctuations and anomalous temperature behavior of conductance amplitudes are predicted.

  7. New insights into the mechanism of electron transfer within flavohemoglobins: tunnelling pathways, packing density, thermodynamic and kinetic analyses.

    Czech Academy of Sciences Publication Activity Database

    El Hammi, E.; Houée-Lévin, Ch.; ?ezá?, Jan; Lévy, B.; Demachy, I.; Baciou, L.; de la Lande, A.

    2012-01-01

    Ro?. 14, ?. 40 (2012), s. 13872-13880. ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : metalloenzymes * flavohemoglobin * electron transfer * monooxygenase Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

  8. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; SØrensen, B.S.

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified by the strain-induced heavy-hole/light-hole splitting.

  9. Enhancing metal-insulator-insulator-metal tunnel diodes via defect enhanced direct tunneling

    International Nuclear Information System (INIS)

    Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al2O3-Ta2O5 bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current versus voltage behavior. These improvements are due to defect enhanced direct tunneling in which electrons transport across the Ta2O5 via defect based conduction before tunneling directly through the Al2O3, effectively narrowing the tunnel barrier. Conduction through the device is dominated by tunneling, and operation is relatively insensitive to temperature.

  10. Tunneling conductance in gapped graphene-based normal metal-insulator-superconductor junctions: Case of massive Dirac electrons

    Energy Technology Data Exchange (ETDEWEB)

    Goudarzi, H., E-mail: h.goudarzi@urmia.ac.i [Department of Physics, Faculty of Science, Urmia University, P.O. Box 165, Urmia (Iran, Islamic Republic of); Sedghi, H.; Khezerlou, M.; Mabhouti, Kh. [Department of Physics, Faculty of Science, Urmia University, P.O. Box 165, Urmia (Iran, Islamic Republic of)

    2010-12-01

    We study the quantum transport property in a gapped graphene-based normal metal-insulator-superconductor junctions (NG/IG/SG), in the limit of a thin barrier. The charged fermions in NG/IG/SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance's in terms of some different electrostatic superconductor, U{sub 0} and barrier, V{sub 0} potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG (E{sub FN} and E{sub FN} + U{sub 0}, respectively), energy gap in graphene (2mv{sub F}{sup 2}) and superconducting order parameter, {Delta}, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take |E{sub FN}-mv{sub F}{sup 2}|{yields}0, it becomes as a step function of V{sub 0}. This behavior of charge transportation can be considered as a nano switch.

  11. Origin of tunneling spin polarization

    International Nuclear Information System (INIS)

    Full text: The relationship of the spin polarization of current tunneling from a ferromagnetic material through a tunnel barrier to its magnetization is of considerable current interest, particularly with regard to the development of magnetic tunnel junctions with high tunneling magnetoresistance suitable for magnetic memory and sensor applications 1. The tunneling spin polarization (TSP) can be directly measured using superconducting tunneling spectroscopy (STS) or inferred from measurements of tunneling magnetoresistance (TMR). The TSP depends not only on the ferromagnetic material but also on the tunneling barrier. Using crystalline (100) oriented MgO tunnel barriers and bcc CoFe electrodes, TSP values exceeding 85% are found from STS studies at 0.25 K with TMR values greater than 300% at 5K2. The same ferromagnetic electrodes using conventional amorphous alumina tunnel barriers exhibit TSP values of only ?50%. In these cases the sign of TSP is positive corresponding to the preferential tunneling of majority spin electrons. However, using magnetic electrodes formed from the ferrimagnetic rare-earth transition-metal alloys, such as Co-Gd, we show that the sign of the TSP and TMR can be either positive or negative depending on the composition of the alloy and temperature. For alloys of Co and Fe with Pt and Pd we show that the TSP is strongly influenced by bonding at the tunnel barrier/ ferromagnetic electrode interface. In particular, we compare resultsrface. In particular, we compare results for CoPt alloys with AlN and Al2O3 tunnel barriers. For AlN barriers the TSP decreases linearly with increasing Pt content whereas for Al2O3 tunnel barriers the TSP has only a weak dependence on Pt content for up to ?50 atomic % Pt. These results can be understood as a consequence of stronger Co - oxygen bonds as compared to Pt - oxygen bonds. References: 1. S. S. P. Parkin, X. Jiang, C. Kaiser, et al., Proc. IEEE 91, 661 (2003). 2 . S. P. Parkin, C. Kaiser, A. Panchula, et al., Nature Mater. 3, 862 (2004)

  12. Wind Tunnel

    Science.gov (United States)

    Lawrence Hall of Science

    2009-01-01

    Scientists use enormous wind tunnels to test the design of planes, helicopters, even the Space Shuttle. In this simulation activity, learners create a miniature wind tunnel test by blowing air with a fan or blow dryer through a large tube, then flying paper airplanes, helicopters and other folded paper models in the "wind." Unless the source of the air is a fan that stands on its own, for example, more than one person will be needed to do the activity.This activity can be combined with the Helicopter Twirl, Parachute Drop and Boomerang activities, also found on the Lawrence Hall of Science Kids Site.

  13. Achieving Resource Conservation in Electronic Waste Management: A Review of Options Available to Developing Countries

    Directory of Open Access Journals (Sweden)

    Innocent Chidi Nnorom

    2007-01-01

    Full Text Available Large quantities of waste electronic devices (e-waste at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in developing countries considering the near absence of state-of-the-art recycling facilities in these countries. Life extension through product and component reuse is especially critical to electronic products because in recent years, electronics have increased in technological complexity, with new product innovations and ever shortening product life expectancy. For many products, environmentalists assume that reuse is environmentally beneficial because it replaces the manufacturing and purchase of new goods. However, on the contrary, manufacturers may oppose this type of reuse for the same reason. There is an urgent need to control the trans-boundary movement of electronic scrap especially to countries without established recycling facilities. Importations of secondhand electronics make such devices available to those who cannot afford new products. However, an international method of testing and certification is needed to ensure that exported secondhand devices are functional. Establishment of formal recycling facilities for e-waste in the developing countries will ensure resource reutilization with both economical and ecological gains. This study reviews options available in working towards eco-efficient management of e-waste in developing countries in the light of the present low-end management practices.

  14. Achieving Resource Conservation in Electronic Waste Management: A Review of Options Available to Developing Countries

    Science.gov (United States)

    Chidi Nnorom, Innocent; Osibanjo, Oladele; Onyedikachi Nnorom, Stanley

    Large quantities of waste electronic devices (e-waste) at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in developing countries considering the near absence of state-of-the-art recycling facilities in these countries. Life extension through product and component reuse is especially critical to electronic products because in recent years, electronics have increased in technological complexity, with new product innovations and ever shortening product life expectancy. For many products, environmentalists assume that reuse is environmentally beneficial because it replaces the manufacturing and purchase of new goods. However, on the contrary, manufacturers may oppose this type of reuse for the same reason. There is an urgent need to control the trans-boundary movement of electronic scrap especially to countries without established recycling facilities. Importations of secondhand electronics make such devices available to those who cannot afford new products. However, an international method of testing and certification is needed to ensure that exported secondhand devices are functional. Establishment of formal recycling facilities for e-waste in the developing countries will ensure resource reutilization with both economical and ecological gains. This study reviews options available in working towards eco-efficient management of e-waste in developing countries in the light of the present low-end management practices.

  15. Electric transport across Sr1-xLaxCuO2/Au/Nb planar tunnel junctions and x-ray photoelectron and Auger-electron spectroscopy on Sr1-xLaxCuO2 thin films

    International Nuclear Information System (INIS)

    Thin-film planar tunnel junctions with the electron-doped infinite-layer superconductor Sr1-xLaxCuO2 (SLCO) with x?0.15 as bottom electrode, a thin Au interlayer, and Nb as top electrode were fabricated and characterized. Measurements of electric transport across these junctions provide information on the interface and surface properties of the SLCO thin films. No Cooper pair tunneling is observed; however, nonlinear current-voltage characteristics give evidence for quasiparticle (QP) tunneling across a thin insulating SLCO barrier at the SLCO/Au interface, with a single gap value ?1.4 meV, originating from superconducting Nb. The absence of a superconducting SLCO gap in the QP conductance curves indicates a thin normal-conducting SLCO layer below the insulating SLCO barrier. To examine its origin, x-ray photoelectron spectroscopy (XPS) and x-ray Auger-electron spectroscopy (XAES) on SLCO thin films were performed. We observe a Cu valence of +1 in the SLCO surface layer (within ?3 nm thickness) and of +2 in deeper regions, as expected for fully oxidized CuO2 planes in the bulk. Hence, the XPS and XAES results for the SLCO films are consistent with the QP tunneling spectra observed for our planar SLCO/Au/Nb junctions.

  16. Tunneling through Quantum Dots with Discrete Symmetries

    OpenAIRE

    Avishai, Yshai; Kikoin, Konstantin

    2008-01-01

    We describe in this short review the influence of discrete symmetries in complex quantum dots on the Kondo co-tunneling through these nano-objects. These discrete symmetries stem from the geometrical structure of the tunneling devices (e.g spatial symmetry of multivalley quantum dot in a tunneling contact with leads). They affect the dynamical symmetry of spin multiplets characterizing the ground state and excitations in quantum dots with definite electron number occupation....

  17. Suppression of tunneling into multiwall carbon nanotubes.

    OpenAIRE

    Bachtold, A.; Jonge, M.; Grove-rasmussen, K.; Mceuen, P. L.; Buitelaar, M.; Scho?nenberger, C.

    2001-01-01

    We have studied tunneling of electrons into multi-wall carbon nanotubes. Nanotube/electrode interfaces with low transparency as well as nanotube/nanotube junctions created with atomic force microscope manipulation have been used. The tunneling conductance goes to zero as the temperature and bias are reduced, and the functional form is consistent with a power law suppression of tunneling as a function of energy. The exponent depends upon sample geometry. The relationship betw...

  18. Enhancement of tunnel magnetoresistance in magnetic tunnel junction by a superlattice barrier

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C. H.; Hsueh, W. J., E-mail: hsuehwj@ntu.edu.tw [Nanomagnetism Group, Department of Engineering Science and Ocean Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road, Taipei 10660, Taiwan (China)

    2014-01-27

    Tunnel magnetoresistance of magnetic tunnel junction improved by a superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The forbidden band of the superlattice is used to predict the low transmission range in the superlattice barrier. By forbidding electron transport in the anti-parallel configuration, the tunnel magnetoresistance is enhanced in the superlattice junction. The results show that the tunnel magnetoresistance ratio for a superlattice magnetic tunnel junction is greater than that for traditional single or double barrier junctions.

  19. Enhancement of tunnel magnetoresistance in magnetic tunnel junction by a superlattice barrier

    International Nuclear Information System (INIS)

    Tunnel magnetoresistance of magnetic tunnel junction improved by a superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The forbidden band of the superlattice is used to predict the low transmission range in the superlattice barrier. By forbidding electron transport in the anti-parallel configuration, the tunnel magnetoresistance is enhanced in the superlattice junction. The results show that the tunnel magnetoresistance ratio for a superlattice magnetic tunnel junction is greater than that for traditional single or double barrier junctions

  20. The influence of electro-mechanical effects on resonant electron tunneling through small carbon nano-peapods

    International Nuclear Information System (INIS)

    The influence of a fullerene molecule trapped inside a single-wall carbon nanotube on resonant electron transport at low temperatures and strong polaronic coupling is theoretically discussed. Strong peak-to-peak fluctuations and anomalous temperature behavior of conductance amplitudes are predicted and investigated. The influence of the chiral properties of carbon nanotubes on transport is also studied

  1. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and monolayer thickness (di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (?DNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ?DNA (dsS-DNA/Au) > ?DNA (MCH/dsS-DNA/Au) > ?DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidizedzed MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

  2. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100 surface investigated by scanning tunneling microscopy and low energy electron diffraction

    Directory of Open Access Journals (Sweden)

    Stefan Gärtner

    2014-09-01

    Full Text Available We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA on the clean and on the oxygen pre-covered Cu(100 surface [referred to as (?2 × 2?2R45° – 2O/Cu(100] by scanning tunneling microscopy (STM and low energy electron diffraction (LEED. Our results confirm the (4?2 × 5?2R45° superstructure of PTCDA/Cu(100 reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100. Quite differently, after preadsorption of oxygen and formation of the (?2 × 2?2R45° – 2O/Cu(100 superstructure on Cu(100, PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  3. In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy

    Directory of Open Access Journals (Sweden)

    Sanduijav B

    2010-01-01

    Full Text Available Abstract Si and Ge growth on the stripe-patterned Si (001 substrates is studied using in situ reflection high-energy electron diffraction (RHEED and scanning tunneling microscopy (STM. During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on “V”-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

  4. Quantum Phase Transitions in Dissipative Tunnel Junctions

    CERN Document Server

    Drewes, S A; Renn, S R; Drewes, Scott; Arovas, Daniel P.; Renn, Scot

    2003-01-01

    The Ueda-Guinea model of a dissipative tunnel junction is investigated. This model accounts for final state effects associated with single-electron tunneling. A quantum phase transition emerges, marking a boundary between insulating (Coulomb blockade) and conducting phases. The system is analyzed by large-N techniques, self-consistent harmonic approximation, and Monte Carlo methods.

  5. A preliminary categorization of end-of-life electrical and electronic equipment as secondary metal resources

    International Nuclear Information System (INIS)

    Highlights: ? End-of-life electrical and electronic equipment (EEE) as secondary metal resources. ? The content and the total amount of metals in specific equipment are both important. ? We categorized 21 EEE types from contents and total amounts of various metals. ? Important equipment types as secondary resources were listed for each metal kind. ? Collectability and possible collection systems of various EEE types were discussed. - Abstract: End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment wpes of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment.

  6. Field emission properties originated from 2D electronics gas successively tunneling for 1D heterostructures of ZnO nanobelts decorated with In2O3 nanoteeth

    International Nuclear Information System (INIS)

    ZnO–In2O3 one-dimensional (1D) nanosized heterostructures constructed by ZnO belts and In2O3 tooth-like particles were self-assembled on single crystal silicon substrate using thermal chemical vapor transport and condensation without being aided by any metal catalyst. The morphology, structure, and composition of the as-synthesized 1D heterostructures were analyzed in detail. The widths of the ZnO nanobelts ranged from several tens of nanometers to one micrometer, and the lengths ranged from several tens to one hundred of micrometers. In2O3 tooth-like nanoparticles with sizes of about 50–100 nm were found grown at two edges of ZnO nanobelts. ZnO nanobelts grew along [101bar 0] direction, whereas In2O3 nanoteeth grew along [311bar], [31bar 1], [3bar 1bar 1], and [3bar 11bar] directions so as to form rhombus-shaped structures. The growth mechanism of the nanosized heterostructures was discussed on the basis of the vapor–solid process and polar surface effect of ZnO nanobelts. Field emission characteristics of the as-prepared heterostructures were measured and explained by energy band theory of heterostructure in detail. It is important to note that the 2D electronics gas (2DEG) was formed between the ZnO energy band bending down and the interface of the heterostructure. The successive tunneling of 2DEG that took place from ZnO to In2O3 and then from InO3 and then from In2O3 to vacuum was the main reason resulting in electronics emission for the nanosized heterostructures in the process of field emission.

  7. Review of material recovery from used electric and electronic equipment-alternative options for resource conservation.

    Science.gov (United States)

    Friege, Henning

    2012-09-01

    For waste from electric and electronic equipment, the WEEE Directive stipulates the separate collection of electric and electronic waste. As to new electric and electronic devices, the Restriction of Hazardous Substances (RoHS) Directive bans the use of certain chemicals dangerous for man and environment. From the implementation of the WEEE directive, many unsolved problems have been documented: poor collection success, emission of dangerous substances during collection and recycling, irretrievable loss of valuable metals among others. As to RoHS, data from the literature show a satisfying success. The problems identified in the process can be reduced to some basic dilemmas at the borders between waste management, product policy and chemical safety. The objectives of the WEEE Directive and the specific targets for use and recycling of appliances are not consistent. There is no focus on scarce resources. Extended producer responsibility is not sufficient to guarantee sustainable waste management. Waste management reaches its limits due to problems of implementation but also due to physical laws. A holistic approach is necessary looking at all branch points and sinks in the stream of used products and waste from electric and electronic equipment. This may be done with respect to the general rules for sustainable management of material streams covering the three dimensions of sustainable policy. The relationships between the players in the field of electric and electronic devices have to be taken into account. Most of the problems identified in the implementation process will not be solved by the current amendment of the WEEE Directive. PMID:22993131

  8. Classical Tunneling

    OpenAIRE

    Cohn, Arthur; Rabinowitz, Mario

    2003-01-01

    A classical representation of an extended body over barriers of height greater than the energy of the incident body is shown to have many features in common with quantum tunneling as the center-of-mass literally goes through the barrier. It is even classically possible to penetrate any finite barrier with a body of arbitrarily low energy if the body is sufficiently long. A distribution of body lengths around the de Broglie wavelength leads to reasonable agreement with the qu...

  9. Quasi-particle Tunneling Through a Barrier in the Fractional Quantum Hall Regime

    OpenAIRE

    Shopen, Elad; Gefen, Yuval; Meir, Yigal

    2005-01-01

    Tunneling of fractionally charged quasi-particles (QPs) through a barrier is considered in the context of a multiply connected geometry. In this geometry global constraints do not prohibit such a tunneling process. The tunneling amplitude is evaluated and the crossover from mesoscopic QP-dominated to electron-dominated tunneling as the system's size is increased is found. The presence of disorder enhances both electron and QP tunneling rates.

  10. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... typically associated with carpal tunnel syndrome, but we'd like to point out today that carpal tunnel ... so all keyboard users are not somebody who'd develop carpal tunnel syndrome, and just because you' ...

  11. Carpal Tunnel Syndrome

    Science.gov (United States)

    ... Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ligament and bones ... from irritated tendons or other swelling narrows the tunnel and causes the nerve to be compressed. Symptoms ...

  12. Use of Electronic Information Resources and Research Output by Academic Staff in Private Universities in Ogun State, Nigeria

    Directory of Open Access Journals (Sweden)

    Itunu Bamidele

    2012-06-01

    Full Text Available The study examined the use of electronic information resources and research output by academic staff in private universities in Ogun state, Nigeria. Three private universities were selected out of the nine private universities in Ogun state. These universities are Crescent University, Abeokuta, Babcock University, Ilishan-Remo, and Redeemers’ University, Mowe, all in Ogun State, Nigeria. Purposive sampling method was used to investigate respondents. The instrument used for data collection was structured questionnaire. 225 copies of the questionnaire were administered at Babcock University and 144 were retrieved. 88 at Crescent University and 80 were retrieved, while 215 at the Redeemers’ University and 130 were retrieved. The research looked at the extent with which electronic information resources were used in the private universities in Ogun State, using the three universities as sample. A total of 528 copies of the questionnaire were distributed to the respondents at the three universities and a valid number of 354 (66% questionnaires were retrieved and analyzed. The questionnaire was designed using nominal and likert scales. The study revealed that most of the academic staff from the three private universities knew and used electronic information resources for their research work as shown on Tables 5, 6, 7 and 8. Findings from Tables 8 and 9 indicate that most of respondents from the three private universities have published their articles and presented papers with the use of electronic information resources. The study also revealed on Table 6 that effective use of electronic information resources contribute to the academics’ research output hence 329 (92.9% of the total respondents supported that view. It is imperative to state here that lack of personal computer and erratic power supply among others are major constraints that inhibit use of electronic information resources in the three private universities which invariably affects their research output. The researchers recommended that private universities in Nigeria expedite action in the area of improving access to electronic information resources through provision of subsidized computers and improved electricity supply in their various universities. Moreso, academic staff are advised to acquire computer skills, learn and relearn to navigate and utilize the vast available electronic information resources on the internet to achieve better research output.
    Key words: Electronic information resources; Research output; Academics; Information access; Information skill; ICT; Electronic journal; Private university; Ogun state

  13. Two vertically coupled quantum rings with tunneling

    Scientific Electronic Library Online (English)

    L. K., Castelano; G.-Q., Hai; B., Partoens; F. M., Peeters.

    2006-09-01

    Full Text Available We study the effect of tunneling on the electronic structure of two vertically coupled quantum rings within the spin density functional theory. The ground state configurations of the coupled rings are obtained for a system with 10 electrons as a function of the ring radius and the inter-ring distanc [...] e. For small ring radius, our results recover those of coupled quantum dots. For large ring radius, new ground state configurations are found in the strong tunneling regime.

  14. Electronic Human Resource Management (e-HRM of Hotel Business in Phuket

    Directory of Open Access Journals (Sweden)

    Kitimaporn Choochote

    2015-04-01

    Full Text Available This research aims to study the pattern of the electronic human resources management (e-HRM of the hotel business in Phuket. The study is conducted with the implementation of field data and in-depth interview of hotels’ HR managers. In consequence, the study reveals that the hotel business has applied the use of the e-HRM varying in job recruitment (15 percent, employee engagement (55 percent, organizational file structure (10 percent, idea and creativity exchanges (38 percent and assessment system (6 percent. However, considered as 100 percent, the hotel business has not prepared to apply the use of the e-HRM in salary system, learning and training program, welfare allocation and career development.

  15. Electronic tracking of human resource skills and knowledge, just in time training, manageable due diligence

    Energy Technology Data Exchange (ETDEWEB)

    Kolodziej, M.A. [Quick Test International Inc., (Canada). Canadian Technology Human Resource Board; Baker, O. [KeySpan Energy Canada, Calgary, AB (Canada)

    2001-06-01

    KeySpan Energy Canada is in the process of obtaining recognition of various occupational profiles including pipeline operators, inspectors, and field and plant operators from various certifying organizations. The process of allowing individuals to obtain certification is recognized by Canadian Technology Human Resources Board as a step towards national standards for technologists and technicians. Proven competency is a must for workers in todays oil industry in response to increasingly stringent government safety regulations, environmental concerns and high public scrutiny. Quick Test international Inc. has developed a management tool in collaboration with end users at KeySpan Energy Canada. It is an electronic, Internet based competency tool for tracking personal competencies and maintaining continued competency. Response to the tool has been favourable. 2 refs., 4 figs.

  16. Domino Tunneling.

    Science.gov (United States)

    Schreiner, Peter R; Wagner, J Philipp; Reisenauer, Hans Peter; Gerbig, Dennis; Ley, David; Sarka, János; Császár, Attila G; Vaughn, Alexander; Allen, Wesley D

    2015-06-24

    Matrix-isolation experiments near 3 K and state-of-the-art quantum chemical computations demonstrate that oxalic acid [1, (COOH)2] exhibits a sequential quantum mechanical tunneling phenomenon not previously observed. Intensities of numerous infrared (IR) bands were used to monitor the temporal evolution of the lowest-energy O-H rotamers (1cTc, 1cTt, 1tTt) of oxalic acid for up to 19 days following near-infrared irradiation of the matrix. The relative energies of these rotamers are 0.0 (1cTc), 2.6 (1cTt), and 4.0 (1tTt) kcal mol(-1). A 1tTt ? 1cTt ? 1cTc isomerization cascade was observed with half-lives (t1/2) in different matrix sites ranging from 30 to 360 h, even though the sequential barriers of 9.7 and 10.4 kcal mol(-1) are much too high to be surmounted thermally under cryogenic conditions. A general mathematical model was developed for the complex kinetics of a reaction cascade with species in distinct matrix sites. With this model, a precise, global nonlinear least-squares fit was achieved simultaneously on the temporal profiles of nine IR bands of the 1cTc, 1cTt, and 1tTt rotamers. Classes of both fast (t1/2 = 30-50 h) and slow (t1/2 > 250 h) matrix sites were revealed, with the decay rate of the former in close agreement with first-principles computations for the conformational tunneling rates of the corresponding isolated molecules. Rigorous kinetic and theoretical analyses thus show that a "domino" tunneling mechanism is at work in these oxalic acid transformations. PMID:26027801

  17. Self-assembled monolayers of radical molecules physisorbed on HOPG(0 0 0 1) substrate studied by scanning tunnelling microscopy and electron paramagnetic resonance techniques

    International Nuclear Information System (INIS)

    In this paper, we present a combined STM and EPR study on the adsorption and self-organization of monolayers formed from 2-(14-Carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16DS) and 4',4'-Dimethylspiro(5?-cholestane-3,2'-oxazolidin)-3'-yloxy (CSL) adsorbed on a highly oriented pyrolitic graphite HOPG(0 0 0 1) substrate. Both 16DS and CSL molecules are persistent free radicals containing a paramagnetic doxyl group. The STM measurements of 16DS on HOPG(0 0 0 1) were performed at the liquid-solid interface while the studies of CSL on HOPG(0 0 0 1) were carried out under ultrahigh vacuum conditions. It was found that the 16DS molecules on the HOPG(0 0 0 1) surface form a highly-ordered monolayer with a domain structure. The high-resolution STM images show structural details of 16DS molecules on HOPG(0 0 0 1) revealing the paramagnetic doxyl group. In contrast, CSL molecules on HOPG(0 0 0 1) form a well-ordered monolayer without domain structure. The EPR results indicate that both compounds deposited on HOPG(0 0 0 1) substrate are not reduced and retain their paramagnetic character. We believe that the molecular systems described can be used in single spin detection experiments using an electron spin noise-scanning tunnelling microscopy (ESN-STM) technique. In particular, the possibility of obtaining contrast spin signals from the paramagnetic and diamagnetic parts of molecules increases the significance of our results.s.

  18. Proton nuclear magnetic resonance studies of hydrogen diffusion and electron tunneling in Ni-Nb-Zr-H glassy alloys

    Energy Technology Data Exchange (ETDEWEB)

    Niki, Haruo; Okuda, Hiroyuki; Oshiro, Morihito; Yogi, Mamoru [Department of Physics, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213 (Japan); Seki, Ichiro; Fukuhara, Mikio [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2012-06-15

    Using the Fourier transform of the echo envelope, the proton line shapes, spin-lattice relaxation time, and spin-spin relaxation time have been measured in a (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} glassy alloy at 1.83 T ({approx}78 MHz) and at temperatures between 1.8 and 300 K. First, the spectral line width decreases abruptly between 1.8 and 2.1 K. Next, it remains almost constant at 13 kHz up to {approx}150 K. Finally, the line width decreases as the temperature increases from {approx}150 to 300 K. The initial decrease in the spectral line width is ascribed to the distribution of the external field, which is caused by the penetration of vortices in the superconducting state. The subsequent leveling off in the spectral line width is ascribed to the dipole-dipole interaction between protons when hydrogen atoms are trapped into vacancies among the Zr-centered icosahedral Zr{sub 5}Ni{sub 5}Nb{sub 3} clusters. The final decrease in the spectral line width is ascribed to the motional narrowing of the width that is caused by the movement of hydrogen atoms. The temperature dependences of the spin-lattice and spin-spin relaxation time showed that at temperature above 150 K and the activation energy of 8.7 kJ/mol allowed the hydrogen atoms to migrate among the clusters. The distance between the hydrogen atoms is estimated to be 2.75 A. Hydrogen occupancies among clusters in the (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} glassy alloy play an important role in the diffusion behavior and in the electronic properties of this alloy.

  19. Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2?y}Se{sub 2} single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru; Presnov, D. E. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 1(2), Leninskie Gory, GSP-1, Moscow 119991 (Russian Federation); Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Ovchenkov, Y. A. [Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Belosludov, R. [Institute for Materials Research, Tohoku University, 980-8577 Sendai (Japan); Boltalin, A. I.; Liu, M.; Morozov, I. V. [Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Nejo, H. [National Institute for Material Science, Tsukuba 305-0047 (Japan); Vasiliev, A. N. [Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002 (Russian Federation); National University of Science and Technology ' MISiS' , Moscow 119049 (Russian Federation)

    2014-07-28

    We investigated the microstructure of the iron selenide superconductor (K{sub 0.7}Na{sub 0.3})Fe{sub 2?y}Se{sub 2} with a T{sub c}?=?32?K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.

  20. Electronic characterization of LaAlO{sub 3}-SrTiO{sub 3} interfaces by scanning tunneling spectroscopy; Elektronische Charakterisierung von LaAlO{sub 3}-SrTiO{sub 3}-Grenzflaechen mittels Rastertunnelspektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Breitschaft, Martin

    2010-10-22

    When LaAlO{sub 3} is epitaxially grown on TiO{sub 2}-terminated SrTiO{sub 3}, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO{sub 3} and SrTiO{sub 3}, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO{sub 3}-SrTiO{sub 3} interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  1. Tunneling technologies for the collider ring tunnels

    International Nuclear Information System (INIS)

    The Texas site chosen for the Superconducting Super Collider has been studied, and it has been determined that proven, conventional technology and accepted engineering practice are suitable for constructing the collider tunnels. The Texas National Research Laboratory Commission report recommended that two types of tunneling machines be used for construction of the tunnels: a conventional hard rock tunnel boring machine (TBM) for the Austin chalk and a double shielded, rotary TBM for the Taylor marl. Since the tunneling machines usually set the pace for the project, efficient planning, operation, and coordination of the tunneling system components will be critical to the schedule and cost of the project. During design, tunneling rate prediction should be refined by focusing on the development of an effective tunneling system and evaluating its capacity to meet or exceed the required schedules. 8 refs., 13 figs

  2. The electronic encapsulation of knowledge in hydraulics, hydrology and water resources

    Science.gov (United States)

    Abbott, Michael B.

    The rapidly developing practice of encapsulating knowledge in electronic media is shown to lead necessarily to the restructuring of the knowledge itself. The consequences of this for hydraulics, hydrology and more general water-resources management are investigated in particular relation to current process-simulation, real-time control and advice-serving systems. The generic properties of the electronic knowledge encapsulator are described, and attention is drawn to the manner in which knowledge 'goes into hiding' through encapsulation. This property is traced in the simple situations of pure mathesis and in the more complex situations of taxinomia using one example each from hydraulics and hydrology. The consequences for systems architectures are explained, pointing to the need for multi-agent architectures for ecological modelling and for more general hydroinformatics systems also. The relevance of these developments is indicated by reference to ongoing projects in which they are currently being realised. In conclusion, some more general epistemological aspects are considered within the same context. As this contribution is so much concerned with the processes of signification and communication, it has been partly shaped by the theory of semiotics, as popularised by Eco ( A Theory of Semiotics, Indiana University, Bloomington, 1977).

  3. Usage of Electronic Resources at Dr T.P.M. Library, Madurai Kamaraj University: A Case Study

    Directory of Open Access Journals (Sweden)

    S. Thanuskodi

    2011-11-01

    Full Text Available Information technology (IT has thrown a new challenge to the libraries. The technology has shown a great impact on the services of the libraries. Libraries use IT for better services and satisfying diverse user needs. Libraries have transformed into digital and virtual libraries where books, journals, and magazines have changed into e-books, e-journals, and e-zines. This has increased the global dissemination of information. Electronic resources (e-resources are easily accessible in the remote areas. The e-resources solve storage problems and control the flood of information. Print sources are being digitised. There is a great need to study the use of e-resources and investigate the factors that are a hindrance to their use. The present study is an attempt to examine the usage of electronic resources at Dr T.P.M. Library, Madurai Kamaraj University. Study revealed that MPhil students respondents took the first position in their overall methods of searching e-resources, postgraduate student respondents the second position, PhD Scholar respondents the last position. The study confirmed that respondents were aware of the e-resources and various types of e-resources, e-database, and e-journals. The study recommended the improvement in the access facilities with high internet speed and subscription to more e-resources at Dr T.P.M. Library, Madurai Kamaraj University.

  4. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires; Aufbau einer Vierspitzen-Rastertunnelmikroskop/Rasterelektronenmikroskop-Kombination und Leitfaehigkeitsmessungen an Silizid Nanodraehten

    Energy Technology Data Exchange (ETDEWEB)

    Zubkov, Evgeniy

    2013-09-01

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement with a gate has provided the resistance of the nanowire. From the dimensions of the nanowire the resistivity was calculated. The obtained resistivity was found to be in agreement with literature values. In addition, the contact resistances of the tunneling tips on the silicide nanowires were determined.

  5. Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules

    CERN Document Server

    Iancu, V; Iancu, Violeta; Hla, Saw-Wai

    2006-01-01

    Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning-tunneling-microscope manipulation and spectroscopy on a gold substrate at 4.6 K. The chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by a support of four CH3 groups. By injecting tunneling electrons from the STM-tip, we are able to bend the phytyl-chain, which enable switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunnelling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.

  6. Instantons revisited: dynamical tunnelling and resonant tunnelling

    CERN Document Server

    Deunff, Jérémy Le

    2009-01-01

    Starting from trace formulae for the tunnelling splittings (or decay rates) analytically continued in the complex time domain, we obtain explicit semiclassical expansions in terms of complex trajectories that are selected with appropriate complex-time paths. We show how this instanton-like approach, which takes advantage of an incomplete Wick rotation, accurately reproduces tunnelling effects not only in the usual double-well potential but also in situations where a pure Wick rotation is insufficient, for instance dynamical tunnelling or resonant tunnelling. Even though only one-dimensional autonomous Hamiltonian systems are quantitatively studied, we discuss the relevance of our method for multidimensional and/or chaotic tunnelling.

  7. SAGES: a suite of freely-available software tools for electronic disease surveillance in resource-limited settings.

    Science.gov (United States)

    Lewis, Sheri L; Feighner, Brian H; Loschen, Wayne A; Wojcik, Richard A; Skora, Joseph F; Coberly, Jacqueline S; Blazes, David L

    2011-01-01

    Public health surveillance is undergoing a revolution driven by advances in the field of information technology. Many countries have experienced vast improvements in the collection, ingestion, analysis, visualization, and dissemination of public health data. Resource-limited countries have lagged behind due to challenges in information technology infrastructure, public health resources, and the costs of proprietary software. The Suite for Automated Global Electronic bioSurveillance (SAGES) is a collection of modular, flexible, freely-available software tools for electronic disease surveillance in resource-limited settings. One or more SAGES tools may be used in concert with existing surveillance applications or the SAGES tools may be used en masse for an end-to-end biosurveillance capability. This flexibility allows for the development of an inexpensive, customized, and sustainable disease surveillance system. The ability to rapidly assess anomalous disease activity may lead to more efficient use of limited resources and better compliance with World Health Organization International Health Regulations. PMID:21572957

  8. Tunneling of Macroscopic Universes

    OpenAIRE

    Conradi, Heinz-Dieter

    1996-01-01

    The meaning of `tunneling' in a timeless theory such as quantum cosmology is discussed. A recent suggestion of `tunneling' of the macroscopic universe at the classical turning point is analyzed in an anisotropic and inhomogeneous toy model. This `inhomogeneous tunneling' is a local process which cannot be interpreted as a tunneling of the universe.

  9. SAGES: A Suite of Freely-Available Software Tools for Electronic Disease Surveillance in Resource-Limited Settings

    OpenAIRE

    Lewis, Sheri L.; Feighner, Brian H.; Loschen, Wayne A.; Wojcik, Richard A.; Skora, Joseph F.; Coberly, Jacqueline S.; Blazes, David L.

    2011-01-01

    Public health surveillance is undergoing a revolution driven by advances in the field of information technology. Many countries have experienced vast improvements in the collection, ingestion, analysis, visualization, and dissemination of public health data. Resource-limited countries have lagged behind due to challenges in information technology infrastructure, public health resources, and the costs of proprietary software. The Suite for Automated Global Electronic bioSurveillance (SAGES) is...

  10. Tunnel visions

    CERN Document Server

    Riordan, Michael; Kolb, Adrienne W.

    2015-01-01

    Starting in the 1950s, US physicists dominated the search for elementary particles; aided by the association of this research with national security, they held this position for decades. In an effort to maintain their hegemony and track down the elusive Higgs boson, they convinced President Reagan and Congress to support construction of the multibillion-dollar Superconducting Super Collider project in Texas-the largest basic-science project ever attempted. But after the Cold War ended and the estimated SSC cost surpassed ten billion dollars, Congress terminated the project in October 1993. Drawing on extensive archival research, contemporaneous press accounts, and over one hundred interviews with scientists, engineers, government officials, and others involved, Tunnel Visions tells the riveting story of the aborted SSC project. The authors examine the complex, interrelated causes for its demise, including problems of large-project management, continuing cost overruns, and lack of foreign contributions. In doi...

  11. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern

    Energy Technology Data Exchange (ETDEWEB)

    Welter, B.

    2007-12-07

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of H{sub c2}(T) respectively H{sub c2}(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown.

  12. Observation of Unitary Conductance for Resonant Tunneling with Dissipation

    International Nuclear Information System (INIS)

    We investigate tunneling through a resonant level formed in a carbon nanotube quantum dot contacted by resistive metal wires. These contacts create a dissipative environment for the electrons tunneling across the nanotube, thus suppressing the tunneling rate. We study the shape of the resonant peak in the nanotube conductance, with the expectation that the peak width and height, both dependent on the tunneling rate, will be suppressed. Instead, we find that the behavior crucially depends on the ratio of the tunneling rates from the resonant level to the two contacts. We discuss the implication of our findings for a boundary quantum phase transition in this system.

  13. Strong quasi-particle tunneling study in the paired quantum Hall states

    OpenAIRE

    Nomura, Kentaro; Yoshioka, Daijiro

    2001-01-01

    The quasi-particle tunneling phenomena in the paired fractional quantum Hall states are studied. A single point-contact system is first considered. Because of relevancy of the quasi-particle tunneling term, the strong tunneling regime should be investigated. Using the instanton method it is shown that the strong quasi-particle tunneling regime is described as the weak electron tunneling regime effectively. Expanding to the network model the paired quantum Hall liquid t...

  14. Tunneling dynamics in multiphoton ionization and attoclock calibration

    CERN Document Server

    Klaiber, M; Keitel, C H

    2014-01-01

    The intermediate domain of strong-field ionization between the tunneling and the multiphoton regimes is investigated using the strong field approximation and the imaginary-time method. An intuitive model for the dynamics is developed which describes the ionization process within a nonadiabatic tunneling picture with a coordinate dependent electron energy during the under-the-barrier motion. The nonadiabatic effects in the elliptically polarized laser field induce a transversal momentum shift of the tunneled electron wave packet at the tunnel exit, a delayed appearance in the continuum as well as a shift of the tunneling exit towards the ionic core. The latter significantly modifies the Coulomb focusing during the electron excursion in the laser field after exiting the ionization tunnel. We show that nonadiabatic effects are especially large when the Coulomb field of the ionic core is taken into account during the under-the-barrier motion. The simpleman model modified with these nonadiabatic corrections provid...

  15. True Serials: A True Solution for Electronic Resource Management Needs in a Medium-Size Academic Library

    Science.gov (United States)

    Milczarski, Vivian; Garofalo, Denise A.

    2011-01-01

    A desire for more functionality seemed to clash with the fiscal reality of limited funds, but after investigating alternatives, Mount Saint Mary College was able to provide its faculty and students with a more useful and function-rich electronic resource management through a move to a hosted open source service. (Contains 8 figures.)

  16. Paradata for 'Fishing-dependent communities on the Gulf Coast of Florida [electronic resource] : their identification, recent decline and present resilience / by Yu Huang.'

    Science.gov (United States)

    This record contains paradata for the resource 'Fishing-dependent communities on the Gulf Coast of Florida [electronic resource] : their identification, recent decline and present resilience / by Yu Huang.'

  17. Spin Valves and Magnetic Tunnel Junctions

    Science.gov (United States)

    Iversen, Kurt; Pufall, Matthew; Heindl, Ranko

    2011-10-01

    This is a presentation of research conducted through the National Institute of Standards and Technology's Summer Undergraduate Research Fellowship program. A spintronic device is one that uses the electron's magnetic moment (its spin) as well as its charge to perform operations, such as data storage or logic. Many of today's spintronic devices are based on the ``tunneling magnetoresistance'' effect of CoFeB/MgO/CoFeB tunnel junctions. The MgO barrier in devices must be highly uniform and only 1-2 nm thick. Relevant background, including electron spin and tunneling, is supplied. The fabrication, operation, and behavior of spin-valves and magnetic tunnel junctions are described, and applications in Hard Disk Drives, Magnetic Random Access Memory, Magnetic Field Sensors, and Spin-Torque Oscillators are discussed.

  18. Momentum noise in vacuum tunneling transducers

    Science.gov (United States)

    Yurke, B.; Kochanski, G. P.

    1990-04-01

    The vacuum tunneling probe can serve as a sensitive transducer of position into current. The performance of such a transducer is characterized by both the uncertainty in the inferred position ?x and the uncertainty in the momentum transfer ?p during the measurement. For realistic barrier parameters we find that the uncertainty product ?x ?p differs by less than 1% from ?/2. We also calculate the expectation values of the force associated with tunneling electrons. If sufficiently sensitive force measurements can be made, this force can provide information about a surface or an absorbed atom, differing from that provided by the tunneling current.

  19. Light emission in tunneling processes

    International Nuclear Information System (INIS)

    We introduce a new method for mapping and analyzing (with atomic resolution) molecules adsorbed on surfaces. This method relies on the detection of fluorescence from molecules, electronically excited by inelastic tunneling in STM. It may combines the excellent spatial resolution of STM together with the specificity of fluorescence as an analytical tool. We propose to overcome this problem by choosing 'transparent conductors' (such as Indium Tin Oxides-lTO) as the STM substrate. ITO, characterized by a large optical gap, will not quench electronically excited molecules. We have tested our idea to enhance the quantum efficiency of molecular emission on surfaces by using transparent conductors in the tunneling junction. We have constructed large area tunnel-junctions by using the squeezable tunnel-Junction technique. The principle of this technique is to squeeze together smooth flat surfaces separated by a thin spacer. By applying a controlled force, junctions with surface area of thousands of square angstroms are made. We have recorded light emission from bare tunneling surfaces and from surfaces coated with molecules (DCA, DCM and COUMARINE), as a function of the bias voltage in the range of 0-5 volts. Typical tunneling currents are 50 nano ampere. Our main findings are: The bare ITO surface emits light at biasing voltages larger than 4.0 eV which corresponds to electron-hole excitation over the optical gap of ITO. ITO surfaces coated with chromophore molecules have sh coated with chromophore molecules have shown enhanced light emission at a voltage bias which corresponds to the allowed excitations energies in the chromophore. A voltage bias of 2-5 V yielded light emission of 5 * 103 photon/?C. The corresponding metallic surfaces, bare or coated with a chromophore did not show any emission. In order to test the possibility of using this effect for imaging purposes we have replaced one electrode of junction with an ITO coated glass tip of 180 ?m radius. such a tip yield an upper limit of tunneling area of 0.3 ?m diameter. (author) 35 refs

  20. Structural comparison between MgO/Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O interfaces for magnetic tunneling junctions: An Auger electron diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Cantoni, M., E-mail: matteo.cantoni@polimi.it; Boseggia, S.; Petti, D.; Cattoni, A.; Bertacco, R.

    2014-06-01

    Magnetic tunnel junctions based on MgO(0 0 1) barriers and ferromagnetic electrodes, such as Fe/MgO/Fe, represent a very popular and widely investigated subject in the field of spin-electronics because of the large values of magnetoresistance shown by these systems. In this paper, the structural properties of MgO thin films grown onto Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O surfaces, with MgO thickness ranging from 2 to 14 equivalent monolayers, have been investigated by means of Auger electron diffraction. The structural order and the crystal quality of the MgO films result practically independent from the template, the latter being either the clean Fe(0 0 1) surface or the oxidized Fe(0 0 1)–p(1 × 1)O one. This is confirmed by numerical simulations, showing that, apart from the first two MgO layers close to the interface, the structure is unaffected by the choice of the starting surface. By a structural point of view, we can conclude that Fe(0 0 1)–p(1 × 1)O is a good candidate for the role of bottom electrode for the realization of MgO-based magnetic tunnelling junctions, also considering its higher chemical stability and reproducibility if compared to the clean Fe(0 0 1) surface.

  1. Human resource requirements for quality-assured electronic data capture of the tuberculosis case register

    Directory of Open Access Journals (Sweden)

    Hoa Nguyen B

    2012-01-01

    Full Text Available Abstract Background The tuberculosis case register is the data source for the reports submitted by basic management units to the national tuberculosis program. Our objective was to measure the data entry time required to complete and double-enter one record, and to estimate the time for the correction of errors in the captured information from tuberculosis case registers in Cambodia and Viet Nam. This should assist in quantifying the additional requirements in human resources for national programs moving towards electronic recording and reporting. Methods Data from a representative sample of tuberculosis case registers from Cambodia and Viet Nam were double-entered and discordances resolved by rechecking the original case register. Computer-generated data entry time recorded the time elapsed between opening of a new record and saving it to disk. Results The dataset comprised 22,732 double-entered records of 11,366 patients (37.1% from Cambodia and 62.9% from Viet Nam. The mean data entry times per record were 97.5 (95% CI: 96.2-98.8 and 66.2 (95% CI: 59.5-73.0 seconds with medians of 90 and 31 s respectively in Cambodia and in Viet Nam. The percentage of records with an error was 6.0% and 39.0% respectively in Cambodia and Viet Nam. Data entry time was inversely associated with error frequency. We estimate that approximately 118-person-hours were required to produce 1,000 validated records. Conclusions This study quantifies differences between two countries for data entry time for the tuberculosis case register and frequencies of data entry errors and suggests that higher data entry speed is partially offset by requiring revisiting more records for corrections.

  2. Static and dynamic aspects of spin tunnelling in crystalline magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Single-crystal magnetic tunnel junctions employing bcc (100) Fe electrodes and MgO(100) insulating barrier are elaborated by molecular beam epitaxy. The magneto-transport properties are investigated in two extreme regimes. First, for extremely small MgO thickness, we show that the equilibrium tunnel transport in Fe/MgO/Fe systems leads to antiferromagnetic interactions, mediated by the tunnelling of the minority spin interfacial resonance state. Second, for large MgO barrier thickness, the tunnel transport validates specific spin filtering effects in terms of symmetry of the electronic Bloch function and symmetry-dependent wavefunction attenuation in the single-crystal barrier. Within this framework, we present giant tunnel magnetoresistive effects at room temperature (125-160%). Moreover, we illustrate that the interfacial chemical and electronic structure plays a crucial role in the spin filtering. We point out imperfect filtering effects and a strong implication of the minority surface state of Fe on the low voltage variation of tunnel magnetoresistance. The insertion of carbon impurities at the Fe/MgO interface changes radically the voltage response of the tunnel magnetoresistance and activates a resonant tunnelling mechanism via the interfacial resonance state

  3. 30 CFR 77.211 - Draw-off tunnels; stockpiling and reclaiming operations; general.

    Science.gov (United States)

    2010-07-01

    ...tunnels; stockpiling and reclaiming operations; general. 77.211 Section 77.211 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION...OF UNDERGROUND COAL MINES Surface Installations § 77.211 Draw-off tunnels; stockpiling and...

  4. Use and Cost of Electronic Resources in Central Library of Ferdowsi University Based on E-metrics

    Directory of Open Access Journals (Sweden)

    Mohammad Reza Davarpanah

    2012-07-01

    Full Text Available The purpose of this study was to investigate the usage of electronic journals in Ferdowsi University, Iran based on e-metrics. The paper also aimed to emphasize the analysis of cost-benefit and the correlation between the journal impact factors and the usage data. In this study experiences of Ferdowsi University library on licensing and usage of electronic resources was evaluated by providing a cost-benefit analysis based on the cost and usage statistics of electronic resources. Vendor-provided data were also compared with local usage data. The usage data were collected by tracking web-based access locally, and by collecting vender-provided usage data. The data sources were one-year of vendor-supplied e-resource usage data such as Ebsco, Elsevier, Proquest, Emerald, Oxford and Springer and local usage data collected from the Ferdowsi university web server. The study found that actual usage values differ for vendor-provided data and local usage data. Elsevier has got the highest usage degree in searches, sessions and downloads. Statistics also showed that a small number of journals satisfy significant amount of use while the majority of journals were used less frequent and some were never used at all. The users preferred the PDF rather than HTML format. The data in subject profile suggested that the provided e-resources were best suited to certain subjects. There was no correlation between IF and electronic journal use. Monitoring the usage of e-resources gained increasing importance for acquisition policy and budget decisions. The article provided information about local metrics for the six surveyed vendors/publishers, e.g. usage trends, requests per package, cost per use as related to the scientific specialty of the university.

  5. Impurity states and interlayer tunneling in high temperature superconductors

    CERN Document Server

    Martin, I; Zaanen, J

    2002-01-01

    We argue that the Scanning Tunneling Microscope (STM) images of impurity states generated by doping Zn or Ni impurities into Cu-O plane of BSCCO are the result of quantum interference of the impurity signal coming from several distinct paths. An impurity image seen on the surface is greatly affected by interlayer tunneling matrix elements. We find that the easiest tunneling path for an STM electron is to tunnel through the Bi 4$s$ orbital into the Zn or Cu 4$s$ orbital and only then into the Cu $d_{x^2 - y^2}$ orbitals in the plane. This tunneling path leads to the four-fold nonlocal filter of the impurity state in Cu-O plane. The tunneling of carriers occurs similarly to the interlayer tunneling in the pure system. We point out that the filter depends on the particular compound and can be different for YBCO.

  6. Tunneling Time in Ultrafast Science is Real and Probabilistic

    CERN Document Server

    Landsman, Alexandra; Maurer, Jochen; Boge, Robert; Ludwig, André; Heuser, Sebastian; Cirelli, Claudio; Gallmann, Lukas; Keller, Ursula

    2013-01-01

    We compare the main competing theories of tunneling time against experimental measurements using the attoclock in strong laser field ionization of helium atoms. Refined attoclock measurements reveal a real and not instantaneous tunneling delay time over a large intensity regime, using two different experimental apparatus. Only two of the theoretical predictions are compatible within our experimental error: the Larmor time, and the probability distribution of tunneling times constructed using a Feynman Path Integral (FPI) formulation. The latter better matches the observed qualitative change in tunneling time over a wide intensity range, and predicts a broad tunneling time distribution with a long tail. The implication of such a probability distribution of tunneling times, as opposed to a distinct tunneling time, challenges how valence electron dynamics are currently reconstructed in attosecond science. It means that one must account for a significant uncertainty as to when the hole dynamics begin to evolve.

  7. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... tunnel syndrome is a compressive neuropathy, which just means that the nerve is being compressed at the ... tunnel syndrome is something called idiopathic, which simply means that we don't really know where it's ...

  8. Quantum theory of tunneling

    CERN Document Server

    Razavy, Mohsen

    2014-01-01

    In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

  9. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... quickly. In the immed-- sorry, in the intermediate stages of carpal tunnel syndrome, the nerve starts to ... rule out the diagnosis. So back to treatment stages. Early on, the carpal tunnel syndrome is potentially ...

  10. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... on a patient with carpal tunnel syndrome. I'm Dr. Kevin Burton, and I'll be joined ... the causes of carpal tunnel syndrome? And I'm going to actually defer on that question because ...

  11. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... tunnel release, and now we're going to talk a little bit about what carpal tunnel syndrome ... nerve -- with the endoscopic technique. At the last American Society for Surgery of the Hand meeting, one ...

  12. Cubital Tunnel Syndrome

    Science.gov (United States)

    ... Infographics Hand Anatomy Find a Hand Surgeon Cubital Tunnel Syndrome Email to a friend * required fields From * ... to name and customize your collection. DESCRIPTION Cubital Tunnel Syndrome is a condition that involves pressure or ...

  13. Carpal Tunnel Release

    Medline Plus

    Full Text Available CARPAL TUNNEL RELEASE HARTFORD HOSPITAL HARTFORD, CONNECTICUT December 11, 2006 00:00:11 ANNOUNCER: Over the next hour, live ... in Hartford, Connecticut, see surgery to correct carpal tunnel syndrome. When the median nerve in the carpal ...

  14. Carpal Tunnel Surgery

    Science.gov (United States)

    Carpal Tunnel Surgery Broward Health Medical Center Fort Lauderdale, FL April 14, 2012 My name is Deepak Kapila, and ... going to be a release of a carpal tunnel, which is carried out for the condition of ...

  15. Carpal Tunnel Surgery

    Medline Plus

    Full Text Available Carpal Tunnel Surgery Broward Health Medical Center Fort Lauderdale, FL April 14, 2012 My name is Deepak Kapila, and ... going to be a release of a carpal tunnel, which is carried out for the condition of ...

  16. Rocket Wind Tunnel

    Science.gov (United States)

    NASA

    2012-05-15

    In this activity, learners evaluate the potential performance of air rockets placed inside a wind tunnel. Learners measure the rocket's resistance to the flow of air in the tunnel and use the data to construct better rockets. The wind tunnel is prepared by the educator before the activity, but can be built by learners with adult supervision. This lesson plan includes instructions on how to build and use a wind tunnel, extensions, and sample data sheets.

  17. Major SSC tunneling begins

    International Nuclear Information System (INIS)

    In Texas, work has been completed on the first on the Superconducting Supercollider's major shafts. Now a boring machine has started driving the fifty-four mile elliptical accelerator tunnel. To date, contracts let for the tunnel have come in far below preliminary estimates. Five of the main fourteen foot diameter tunnel contracts have been awarded for a total of 107.4 million dollars, about forty million dollars below estimates. These contracts represent %60 percent of the total tunneling project

  18. Photonic tunneling times

    OpenAIRE

    Nimtz, G.; Enders, A; Spieker, H.

    1994-01-01

    We report on resonant and non-resonant photonic tunneling experiments. Resonant tunneling of wave packets has revealed a light localization, whereas the non-resonant barrier tunneling has corresponded to a zero-time barrier crossing. For a frequency-limited signal the non-resonant tunneling transmission time yielded superluminal group velocities, whereas in the case of a resonant transition the velocities are much slower than c.

  19. Molecular series-tunneling junctions.

    Science.gov (United States)

    Liao, Kung-Ching; Hsu, Liang-Yan; Bowers, Carleen M; Rabitz, Herschel; Whitesides, George M

    2015-05-13

    Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure Ag(TS)/O2C-R1-R2-H//Ga2O3/EGaIn, where Ag(TS) is template-stripped silver and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series-tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the highest occupied molecular orbital (HOMO, which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the Ag(TS)/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series-tunneling junctions can be described by J(V) = J0(V) exp(-?1d1 - ?2d2), where J(V) is the current density (A/cm(2)) at applied voltage V and ?i and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor ?. PMID:25871745

  20. Electronic structure and optical properties of 1.55 µm emitting InAs/InGaAsP quantum dash tunnel injection structures

    International Nuclear Information System (INIS)

    Optical spectroscopy studies have been reported on an application-relevant system emitting at 1.55 µm and consisting of an InGaAsP injector quantum well (QW), separated by a thin InP barrier (of various thicknesses) from InAs elongated quantum dots called quantum dashes (QDash). The investigated systems constitute tunnel injection structures, whose operation principle is the transfer of carriers captured by the injector QW to the QDash layer by means of tunnelling. Numerical calculations in the eight-band kp model with a realistic dash geometry are used in order to determine the energies of confined levels and their wave functions, results of which are then verified by comparison with measured photoreflectance spectra and used to interpret spectroscopic findings. The tunnelling of carriers from QW to QDash layer is evidenced by photoluminescence excitation measurements and further supported by unusual temperature behaviour of PL peaks broadenings. Careful numerical analysis of confined states and their wave functions explains optical properties of investigated samples. The suggestions for the proper design of structures based on the injection of carriers for applications in telecom lasers are given; most importantly it is shown that care must be taken so that the QW does not significantly influence the dash emitter. (paper)

  1. Achieving Resource Conservation in Electronic Waste Management: A Review of Options Available to Developing Countries

    OpenAIRE

    Innocent Chidi Nnorom; Oladele Osibanjo; Stanley Onyedikachi Nnorom

    2007-01-01

    Large quantities of waste electronic devices (e-waste) at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in dev...

  2. Data Resource Profile: Cardiovascular disease research using linked bespoke studies and electronic health records (CALIBER)

    OpenAIRE

    Denaxas, S. C.; George, J.; Herrett, E.; Shah, A. D.; Kalra, D.; Hingorani, A. D.; Kivimaki, M.; Timmis, A. D.; Smeeth, L.; Hemingway, H.

    2012-01-01

    The goal of cardiovascular disease (CVD) research using linked bespoke studies and electronic health records (CALIBER) is to provide evidence to inform health care and public health policy for CVDs across different stages of translation, from discovery, through evaluation in trials to implementation, where linkages to electronic health records provide new scientific opportunities. The initial approach of the CALIBER programme is characterized as follows: (i) Linkages of multiple electronic he...

  3. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... on in carpal tunnel syndrome, there is increased pressure in the carpal tunnel which causes some decreased blood flow to the ... That decreases the actual volume of the carpal tunnel and puts excess pressure on the nerve while we're sleeping and ...

  4. Intention to Use and Actual Use of Electronic Information Resources: Further Exploring Technology Acceptance Model (TAM)

    OpenAIRE

    Tao, Donghua

    2009-01-01

    Following up a previous study that examined public health students’ intention to use e-resources for completing research paper assignments, the present study proposed two models to investigate whether or not public health students actually used the e-resources they intended to use and whether or not the determinants of intention to use predict actual use of e-resources. Focus groups and pre- and post-questionnaires were used to collect data. Descriptive analysis, data screening, and Structu...

  5. Correlated tunneling in intramolecular carbon nanotube quantum dots

    OpenAIRE

    Thorwart, M.; Grifoni, M.; Cuniberti, G.; Postma, H. W. Ch; C Dekker, C.

    2002-01-01

    We investigate correlated electronic transport in single-walled carbon nanotubes with two intramolecular tunneling barriers. We suggest that below a characteristic temperature the long-range nature of the Coulomb interaction becomes crucial to determine the temperature dependence of the maximum {\\it G}$_{max}$ of the conductance peak. Correlated sequential tunneling dominates transport yielding the power law {\\it G}$_{max}$${\\sim}$$_{end–end}$–1}$, typical for tunneling between the ends ...

  6. Single base resolution in tunneling reads of DNA composition

    OpenAIRE

    Huang, Shuo; He, Jin; Chang, Shuai; Zhang, Peiming; Liang, Feng; Li, Shengqin; Tuchband, Michael; Fuhrman, Alexander; Ros, Robert; Lindsay, Stuart

    2010-01-01

    Single-molecule DNA sequencing based on measuring the physical properties of bases as they pass through a nanopore1,2 eliminates the need for the enzymes and reagents used in other approaches. Theoretical calculations indicate that electron tunneling could identify bases in single-stranded DNA, yielding long reads and eliminating enzymatic processing.3–5 It was shown recently that tunneling can sense individual nucleotides6 and nucleosides.7 Here, we show that tunneling electrodes functionali...

  7. Improving sequencing by tunneling with multiplexing and cross-correlations

    OpenAIRE

    Boynton, P.; Balatsky, A. V.; Schuller, I. K.; Di Ventra, M.

    2014-01-01

    Sequencing by tunneling is a next-generation approach to read single-base information using electronic tunneling transverse to the single-stranded DNA (ssDNA) backbone while the latter is translocated through a narrow channel. The original idea considered a single pair of electrodes to read out the current and distinguish the bases [1, 2]. Here, we propose an improvement to the original sequencing by tunneling method, in which $N$ pairs of electrodes are built in series alon...

  8. Visualization of pool boiling from complex surfaces with internal tunnels

    OpenAIRE

    Pastuszko Robert

    2012-01-01

    The paper presents experimental investigations of boiling heat transfer for a system of connected narrow horizontal and vertical tunnels. These extended surfaces, named narrow tunnel structure (NTS), can be applied to electronic element cooling. The experiments were carried out with ethanol at atmospheric pressure. The tunnel external covers were manufactured out of 0.1 mm thick perforated copper foil (hole diameters 0.5 mm), sintered with the mini-fins, formed on the vertical side of the 10 ...

  9. Challenges in the implementation of an electronic surveillance system in a resource-limited setting: Alerta, in Peru

    OpenAIRE

    Soto Giselle; Araujo-Castillo Roger V; Neyra Joan; Fernandez Miguel; Leturia Carlos; Mundaca Carmen C; Blazes David L

    2008-01-01

    Abstract Background Infectious disease surveillance is a primary public health function in resource-limited settings. In 2003, an electronic disease surveillance system (Alerta) was established in the Peruvian Navy with support from the U.S. Naval Medical Research Center Detachment (NMRCD). Many challenges arose during the implementation process, and a variety of solutions were applied. The purpose of this paper is to identify and discuss these issues. Methods This is a retrospective descript...

  10. Integration and interoperability accessing electronic information resources in science and technology: the proposal of Brazilian Digital Library

    OpenAIRE

    Marcondes, Carlos H.; Sayao, Luis Fernando

    2002-01-01

    This paper describes technological and methodological options to achieve interoperability in accessing electronic information resources, available in Internet, in the scope of Brazilian Digital Library in Science and Technology Project - BDL, developed by Brazilian Institute for Scientific and Technical Information - IBICT. It stresses the impact of the Web in the publishing and communication processes in science and technology and also in the information systems and librari...

  11. ‘I’ll just Google it!’: Should lawyers’ perceptions of Google inform the design of electronic legal resources?

    OpenAIRE

    Makri, S.; Blandford, A.; Cox, A. L.

    2007-01-01

    Lawyers, like many user groups, regularly use Google to find information for their work. We present results of a series of interviews with academic and practicing lawyers, where they discuss in what situations they use various electronic resources and why. We find lawyers use Google due to a variety of factors, many of which are related to the need to find information quickly. Lawyers also talk about Google with a certain affection not demonstrated when discussing other r...

  12. Use of Electronic Information Resources and Research Output by Academic Staff in Private Universities in Ogun State, Nigeria

    OpenAIRE

    Itunu Bamidele; Ezinwayi Madukoma; Omeluzor, Saturday U.; Ogbuiyi, Susan U.

    2012-01-01

    The study examined the use of electronic information resources and research output by academic staff in private universities in Ogun state, Nigeria. Three private universities were selected out of the nine private universities in Ogun state. These universities are Crescent University, Abeokuta, Babcock University, Ilishan-Remo, and Redeemers’ University, Mowe, all in Ogun State, Nigeria. Purposive sampling method was used to investigate respondents. The instrument used for data collection w...

  13. The Mouse Tumor Biology Database (MTB): A Central Electronic Resource for Locating and Integrating Mouse Tumor Pathology Data

    OpenAIRE

    Begley, D. A.; Krupke, D. M.; Neuhauser, S. B.; Richardson, J. E.; Bult, C. J.; Eppig, J. T.; Sundberg, J. P.

    2011-01-01

    The Mouse Tumor Biology Database (MTB) is designed to provide an electronic data storage, search, and analysis system for information on mouse models of human cancer. MTB includes data on tumor frequency and latency, strain, germ line and somatic genetics, pathologic notations, and photomicrographs. MTB collects data from the primary literature, other public databases, and direct submissions from the scientific community. MTB is a community resource that provides integrated access to mouse tu...

  14. Investigation into scanning tunnelling luminescence microscopy

    International Nuclear Information System (INIS)

    This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provide information on recombination processes and material properties. The design and construction of a scanning tunnelling luminescence microscope is described in detail. Operating under ambient conditions, the microscope has several novel features, including a new type of miniature inertial slider-based approach motor, large solid-angle light collection optical arrangement and a tip-height regulation system which requires the minimum of operator input. (author)e minimum of operator input. (author)

  15. Computational Role of Collective Tunneling in a Quantum Annealer

    OpenAIRE

    Boixo, Sergio; Smelyanskiy, Vadim N.; Shabani, Alireza; Isakov, Sergei V.; Dykman, Mark; Denchev, Vasil S.; Amin, Mohammad; Smirnov, Anatoly; Mohseni, Masoud; Neven, Hartmut

    2014-01-01

    Quantum tunneling is a phenomenon in which a quantum state traverses energy barriers above the energy of the state itself. Tunneling has been hypothesized as an advantageous physical resource for optimization. Here we present the first experimental evidence of a computational role of multiqubit quantum tunneling in the evolution of a programmable quantum annealer. We develop a theoretical model based on a NIBA Quantum Master Equation to describe the multiqubit dissipative tu...

  16. Student Effort, Media Preference, and Writing Quality when Using Print and Electronic Resources in Expository Writing

    Science.gov (United States)

    Schuh, Kathy L.; Farrell, Courtney A.

    2006-01-01

    The purpose of this study was to analyze the effects of the Internet as a research tool on elementary students' quality of writing, their perceptions of effort expended, and their resource media preference in writing an expository paper. We gathered data from 56 upper-elementary students as they wrote expository papers using print resources

  17. Relationship between Human Resources Management Practices, Transformational Leadership, and Knowledge Sharing on Innovation in Iranian Electronic Industry

    Directory of Open Access Journals (Sweden)

    Mahmoud Manafi

    2015-03-01

    Full Text Available Electronic industry needs innovation to survive, and also to compete internationally. This study examines factors that can enhance technical innovation of companies in the electronic industry of Iran. The main purpose of this study is to examine the relationship between human resource management practices, transformational leadership, knowledge sharing, and innovation of the large and major electronic companies.More specifically, the research attempts to examine whether knowledge sharing mediates the relationship between human resource management practices and transformational leadership with innovation. A quantitative research approach was used in this study. A cross-sectional correlational research design was used.The sample for this study was drawn from a population of 23,704 employees (managers, engineers, and expert technicians of eight largest electronic companies in Iran using stratified sampling method. The sample size was 376.After exploratory Factor Analysis (EFA and confirmatory factor analysis (CFA, structural equation modeling (SEM technique was used to test the hypothetical model. The Findings asserts that only two HRM practices (training and participation and three transformational leadership components (vision, intellectual stimulation and personal recognition have significant impacts on innovation. Besides, knowledge sharing has significant and positive impact on innovation. Out of five HRM practices, training, staffing, participation have significant and positive impacts on knowledge sharing while intellectual stimulation, and personal recognition(as transformational leadership components have significant and positive impacts.Finally, knowledge sharing merely mediated the relationships of training, participation, vision and personal recognition with innovation.

  18. Electronic Phase Separation in Pr1x(Ca, Sr)xMnO3? and Tunneling Magnetoresistance in Sr2FeMoO6

    International Nuclear Information System (INIS)

    In this work, we approach two aspects of the physics of magnetic perovskites presenting colossal magnetoresistance (CMR). Firstly, we go deeply into the phase separation (PS) between the ferromagnetic (FM) metallic state and the antiferro-magnetic (AFM) charge ordered (CO) insulating state, in manganites of the type Pr1x(Ca,Sr)xMnO3?. Secondly, and more briefly, we analyze the problem of the influence of the grain boundary insulating barriers on the tunneling magnetoresistance in the Sr2FeMoO6 double perovskite.The use of different measurement techniques allowed us to make a complete characterization of the PS state in the compounds Pr0.65Ca0.35-ySryMnO3 for 0? y ? 0.20, Pr0.5Sr0.5-zCazMnO3 for z = 0, 0.1 and 0.2 and Pr1-xCax-0.3Sr0.3MnO3 (0.46? x ? 0.54), that were prepared in our laboratory.The structural studies of these materials were performed at room temperature by means of X-ray diffraction. At low temperatures, the phase coexistence was observed by global magnetic techniques, as SQUID magnetometry and neutron diffraction, as well as measurements sensitive to the local magnetic environment, as electron spin resonance (ESR).The electrical characterization, performed through resistivity and thermoelectric power (Seebeck effect) measurements, allowed us to elucidate the characteristics of the metal-insulator transitions, which are directly related to the magnetic properties of the PS state. In Pr0.65Ca0.35-ySryMnO3 compound we studied the effects of the average ionic radius of the A site of the perovskite (A> ) keeping constant the carrier concentration (x = 0.35). This material presents an evolution from a CO insulating phase for small A> (y =0), towards the FM metallic phase for large A> (y = 0.20). In the intermediate region, where a first order metal-insulator transition occurs, the strong competition between both phases induces the PS state in a wide temperature range. In order to quantify this coexistence, we obtained the FM phase fraction (X) as a function of temperature from the magnetization data. The effects of the disorder on the first-order metal-insulator transition is one of the proposed mechanisms for the phase coexistence. Magnetization curves as a function of magnetic field (H) in the PS state show the existence of two dynamic regimes separated by the field Hc, which is interpreted as a critical field for the depinning of domain walls. From the analysis of the thermally activated susceptibility at H c, we estimate the size of the FM clusters as ?130nm, in agreement with the characteristic sizes observed by electron microscopy. The percolative analysis of the conductivity, ? ? (X - Xc)p, indicates that the critical percolation threshold is Xc ? 15.5%, in good agreement with the expected values in three-dimensional systems. On the other hand, the obtained critical exponent p ? 1, is lower than the expected value for these systems (p3D ? 2). This could be related to geometrical effects of the ferromagnetic domains or to the presence of a third two-dimensional phase that we observe in the neutron diffraction experiments. The magnetoresistance also presents very different properties for the samples with a percolated FM phase. As a result of this, to obtain the largest values of CMR it is convenient to prepare samples with a FM phase fraction as close as possible to the critical percolation threshold. In the Pr0.5Ca0.2Sr0.3MnO3-? (? = 0 and 0.01) we studied the effects of the oxygen vacancies on the phase separation. We showed the the vacancies located in the AFM volume generate a local FM polarization in their vicinity, within a radius of ? 1nm. At the same time, this favors the percolation of the metallic phase, inducing a decrease of the resistivity. However, the effect of the vacancies is negligible as compared to the PS already present in the stoichiometric compound. This observation rules out the oxygen vacancies as the root of the origin of the PS phenomenon. Finally, in the ordered double perovskite Sr2FeMoO6 the studies were mainly oriented to the magnetotransport propertie

  19. Resonant tunnelling in a quantum oxide superlattice.

    Science.gov (United States)

    Choi, Woo Seok; Lee, Sang A; You, Jeong Ho; Lee, Suyoun; Lee, Ho Nyung

    2015-01-01

    Resonant tunnelling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunnelling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunnelling behaviour with a clear negative differential resistance. The tunnelling occurred through an atomically thin, lanthanum ?-doped SrTiO3 layer, and the negative differential resistance was realized on top of the bipolar resistance switching typically observed for perovskite oxide junctions. This combined process resulted in an extremely large resistance ratio (?10(5)) between the high and low-resistance states. The unprecedentedly large control found in atomically thin ?-doped oxide superlattices can open a door to novel oxide-based high-frequency logic devices. PMID:26104684

  20. Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

    KAUST Repository

    Useinov, A. N.

    2011-08-24

    We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.