WorldWideScience

Sample records for tunnels electronic resource

  1. Electron-Tunneling Magnetometer

    Science.gov (United States)

    Kaiser, William J.; Kenny, Thomas W.; Waltman, Steven B.

    1993-01-01

    Electron-tunneling magnetometer is conceptual solid-state device operating at room temperature, yet offers sensitivity comparable to state-of-art magnetometers such as flux gates, search coils, and optically pumped magnetometers, with greatly reduced volume, power consumption, electronics requirements, and manufacturing cost. Micromachined from silicon wafer, and uses tunneling displacement transducer to detect magnetic forces on cantilever-supported current loop.

  2. Single Electron Tunneling

    International Nuclear Information System (INIS)

    Financial support for this project has led to advances in the science of single-electron phenomena. Our group reported the first observation of the so-called ''Coulomb Staircase'', which was produced by tunneling into ultra-small metal particles. This work showed well-defined tunneling voltage steps of width e/C and height e/RC, demonstrating tunneling quantized on the single-electron level. This work was published in a now well-cited Physical Review Letter. Single-electron physics is now a major sub-field of condensed-matter physics, and fundamental work in the area continues to be conducted by tunneling in ultra-small metal particles. In addition, there are now single-electron transistors that add a controlling gate to modulate the charge on ultra-small photolithographically defined capacitive elements. Single-electron transistors are now at the heart of at least one experimental quantum-computer element, and single-electron transistor pumps may soon be used to define fundamental quantities such as the farad (capacitance) and the ampere (current). Novel computer technology based on single-electron quantum dots is also being developed. In related work, our group played the leading role in the explanation of experimental results observed during the initial phases of tunneling experiments with the high-temperature superconductors. When so-called ''multiple-gap'' tunneling was reported, the phenomenon was correctly identified by our group as single-electron tunneling in small grains in the material. The main focus throughout this project has been to explore single electron phenomena both in traditional tunneling formats of the type metal/insulator/particles/insulator/metal and using scanning tunneling microscopy to probe few-particle systems. This has been done under varying conditions of temperature, applied magnetic field, and with different materials systems. These have included metals, semi-metals, and superconductors. Amongst a number of results, we have verified that clusters of down to one, two, and three metal atoms can be identified with single-electron techniques. We have also, extended the regime of single-electron phenomenology through the observation of single-electron effects in metal droplets in the high-conductance regime

  3. 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)

  4. Inelastic electron tunneling spectroscopy

    International Nuclear Information System (INIS)

    IETS provides an electronic probe with great sensitivity and resolution for monitoring the vibrational spectra of less-than-monolayer coverages of adsorbed molecular species. Eletronic transitions of large dye molecules and of rare-earth oxides have also been studied by IETS and very recently inelastic electron tunneling has been employed in the design of a tunable light-emitting thin film device. This Proceedings volume provides a comprehensive and up-to-date review of the current state-of-the-art of IETS. A tutorial survey of the techniques and applications of IETS is provided as are discussions of the newest advances in the field. Recent applications of IETS to surface chemistry and catalysis trace substance identification and detection, the study of biological molecules and the study of adhesive materials are included among the papers. Discussions of the IETS theory are also reported. (orig./HT)

  5. 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.

  6. 3e tunneling processes in a superconducting single-electron tunneling transistor

    CERN Document Server

    Hadley, P; Visscher, E H; Lahteenmaki, S; Mooij, J E

    1998-01-01

    A current due to a tunneling event that involves three times the charge of an electron was observed in the current - voltage characteristics of a superconducting single-electron tunneling transistor. In this tunnel event, a Cooper pair tunnels through one tunnel barrier simultaneously with a quasiparticle that tunnels through a second tunnel barrier which is about 0.5 microns distant from the first tunnel barrier. This current was observed in a bias regime where current flow due to sequential quasiparticle tunneling is forbidden due to the Coulomb blockade.

  7. Electron Tunneling in Monolayer and Bilayer Graphene

    OpenAIRE

    WU Di; Chen, Weiqiang; Zhang, Fu-chun

    2008-01-01

    Electron's tunneling through potential barrier in monolayer and bilayer graphene lattices is investigated by using full tight-binding model. Emphasis is placed on the resonance tunneling feature and inter-valley scattering probability. It is shown that normal incidence transmission probabilities for monolayer and bilayer graphene exhibit different properties. Our calculation indicates that valleytronics in graphene systems may be detected, generated and controlled by changin...

  8. Tunneling of electrons through semiconductor superlattices

    Indian Academy of Sciences (India)

    C L Roy

    2002-11-01

    The purpose of the present paper is to report a study of tunneling of electrons through semiconductor superlattices (SSL); specially, we have analysed diverse features of transmission coefficient of SSL. The SSL we have considered is Ga0.7Al0.3As–GaAs which has been drawing considerable attention during the recent past on account of some typical features of its band structure. We have indicated how our results would help fabrication of ultra high speed devices.

  9. Single-electron tunneling. [Microwave scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Ruggiero, S.T.

    1993-01-01

    Pictures using the low-temperature microwave scanning tunneling microscope, have been made of particles and tunneling IV characteristics determined. Strong, sometimes periodic negative differential resistance was observed in small-particle systems. Au and Ag droplets and particles were studied. 4 figs.

  10. 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

  11. 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

  12. Electron tunneling in double quantum dots and rings

    International Nuclear Information System (INIS)

    The electron tunneling in double quantum dot (DQD) is studied by changing of inter-dot distance. Localization of an electron is calculated for each level of the whole spectrum of the confinement states of DQD. For identical QDs the tunneling goes consecutively from high energy levels to the ground state. It is changed essentially when the QDs of the system are non-identical. We show that violation of symmetry of the DQD geometry makes it difficult for the tunneling. For double quantum ring (DQR) we demonstrate that the electron states with the same type of rotation symmetry play an important role for tunneling.

  13. 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.

  14. Quantum Hall Effect: proposed multi-electron tunneling experiment

    International Nuclear Information System (INIS)

    Here we propose a tunneling experiment for the fractional and Integral Quantum Hall Effect. It may demonstrate multi-electron tunneling and may provide information about the nature of the macroscopic quantum states of 2D electronic liquid or solid. (author)

  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. The AAS electronic resource

    Science.gov (United States)

    Boyce, Peter B.; Biemesderfer, Chris; Owens, Evan

    Recent experience is helping to sharpen our understanding of how the electronic world differs from the centuries-old, paper-based communication methods. The electronic future is highly interlinked, with all different types of information being included in the web of available resources. The enhanced ability to interchange information electronically improves the effectiveness of communication. At this time the author community does not make full use of the new capabilities. Most astronomers writing for electronic distribution have been slow to adopt new styles of presentation which exploit the new capabilities inherent in the electronic environment. By working together and sharing the burden, the community's resources can be multiplied. A coordinated distributed effort can yield a much more valuable product than any single person or group. Long term archiving and site maintenance are important responsibilities for publishers of electronic scholarly information. Ensuring access to electronic information into the foreseeable future takes planning from the beginning, and requires cooperation between the publishers, libraries, and other scholarly institutions.

  17. 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.

  18. 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

  19. Educating for Electronic Resources

    Science.gov (United States)

    Grogg, Jill E.

    2008-01-01

    While mission statements for various libraries and information centers necessarily vary, all librarians face "two very pressing charges: make voluminous numbers of electronic resources as visible as possible in a landscape of multiple access points and simultaneously manage all the technology, tasks, and data necessary to facilitate such…

  20. 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

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

    DEFF Research Database (Denmark)

    Ejrnaes, M.; Savolainen, M.; Manscher, M.; Mygind, Jesper

    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 me...

  2. Single-electron tunneling. Technical progress report

    Energy Technology Data Exchange (ETDEWEB)

    Ruggiero, S.T.

    1993-05-01

    Pictures using the low-temperature microwave scanning tunneling microscope, have been made of particles and tunneling IV characteristics determined. Strong, sometimes periodic negative differential resistance was observed in small-particle systems. Au and Ag droplets and particles were studied. 4 figs.

  3. Electronic Resource Management Systems

    Directory of Open Access Journals (Sweden)

    Mark Ellingsen

    2004-10-01

    Full Text Available Computer applications which deal with electronic resource management (ERM are quite a recent development. They have grown out of the need to manage the burgeoning number of electronic resources particularly electronic journals. Typically, in the early years of e-journal acquisition, library staff provided an easy means of accessing these journals by providing an alphabetical list on a web page. Some went as far as categorising the e-journals by subject and then grouping the journals either on a single web page or by using multiple pages. It didn't take long before it was recognised that it would be more efficient to dynamically generate the pages from a database rather than to continually edit the pages manually. Of course, once the descriptive metadata for an electronic journal was held within a database the next logical step was to provide administrative forms whereby that metadata could be manipulated. This in turn led to demands for incorporating more information and more functionality into the developing application.

  4. 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. ...

  5. 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...

  6. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  7. Klein tunneling in graphene: optics with massless electrons

    OpenAIRE

    Allain, P. E.; Fuchs, J.N.

    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...

  8. Tunneling conductance in a system with strong electron correlation

    Directory of Open Access Journals (Sweden)

    Hong J.

    2012-03-01

    Full Text Available We discuss the structure of tunneling conductance, the dI/dV lineshape, observed for a system with strong electron correlation. The structure of the dI/dV lineshape comprises zero-bias peak and two side peaks. We discuss the condition for compressing zero-bias peak and the origin of two side peaks. We explain why the tunneling conductance does not simply reflect the sample density of states in the tunneling experiment for a system with strong electron correlation.

  9. Time of electron tunneling through a potential barrier

    International Nuclear Information System (INIS)

    Problem of mean time of an electron tunnelling in a classically prohibited region is investigated. A natural method for generalizing the classical time-of-flight notion for a quantum-mechanical case is suggested and its application to the tunneling problem through a one-dimensional potential barrier is considered. In separate consideration of passed and reflected particles complex parameters appear which make sense of tunnelling times for passed and reflected particles. Relation of these parameters and angles of electron spin rotation in magnetic field localized in the barrier region was investigated

  10. Wigner time delay for tunneling ionization via the electron propagator

    Science.gov (United States)

    Yakaboylu, Enderalp; Klaiber, Michael; Hatsagortsyan, Karen Z.

    2014-07-01

    Recent attoclock experiments using the attosecond angular streaking technique enabled the measurement of the tunneling time delay during laser-induced strong-field ionization. One of the theoretical models for the tunneling time delay is the Wigner time delay, which is the asymptotic time difference between the quasiclassical and the Wigner trajectories. The latter is derived from the derivative of the phase of the electron steady-state wave function with respect to energy. Here, we present an alternative method for the calculation of the Wigner trajectory by using the fixed-energy propagator. The developed formalism is applied to the nonrelativistic regime as well as to the relativistic regime of the tunnel-ionization process from a zero-range potential. Finally, it is shown that the Wigner time delay is measurable in the near-threshold-tunneling regime within the current state of the momentum spectroscopy via detecting the induced electron momentum shift in a mixture of two gas species.

  11. 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...

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

    DEFF Research Database (Denmark)

    Lagoute, Jerome; Joucken, Frederic; Repain, Vincent; Tison, Yann; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Sporken, Robert; Conrad, Edward H.; Ducastelle, Francois; Palsgaard, Mattias Lau Nøhr; Andersen, Nick Papior; Brandbyge, Mads; Rousset, Sylvie

    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 ...

  13. Inelastic electron tunneling spectroscopy of a single nuclear spin

    OpenAIRE

    Delgado Acosta, Fernando; Fernández Rossier, Joaquín

    2011-01-01

    Detection of a single nuclear spin constitutes an outstanding problem in different fields of physics such as quantum computing or magnetic imaging. Here we show that the energy levels of a single nuclear spin can be measured by means of inelastic electron tunneling spectroscopy (IETS). We consider two different systems, a magnetic adatom probed with scanning tunneling microscopy and a single Bi dopant in a silicon nanotransistor. We find that the hyperfine coupling opens new transport channel...

  14. Attosecond correlation dynamics during electron tunnelling from molecules

    International Nuclear Information System (INIS)

    In this communication, we present an analytical theory of strong-field ionization of molecules, which takes into account the rearrangement of multiple interacting electrons during the ionization process. We show that such rearrangement offers an alternative pathway to the ionization of orbitals more deeply bound than the highest occupied molecular orbital. This pathway is not subject to the full exponential suppression characteristic of direct tunnel ionization from the deeper orbitals. The departing electron produces an 'attosecond correlation pulse' which controls the rearrangement during the tunnelling process. The shape and duration of this pulse are determined by the electronic structure of the relevant states, molecular orientation and laser parameters. (fast track communication)

  15. 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.

  16. Klein tunneling in graphene: optics with massless electrons

    Science.gov (United States)

    Allain, P. E.; Fuchs, J. N.

    2011-10-01

    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-Pérot 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. The current experimental status is also thoroughly reviewed. The Appendix contains the discussion of a one-dimensional toy model that clearly illustrates the difference in Klein tunneling between mono- and bi-layer graphene.

  17. Observation of interdot tunneling process of spin-polarized electrons

    Science.gov (United States)

    Tackeuchi, A.; Nakata, Y.; Sasou, R.; Mase, K.; Kuroda, T.; Yokoyama, N.

    2001-05-01

    We have directly observed the spin-polarized electron tunneling process between double quantum dots (QDs) using spin-dependent time-resolved photoluminescence measurements. The spin relaxation times in isolated In 0.9Al 0.1As Stranski-Krastanow (SK)-mode QDs and InAs SK-mode QDs were measured as 1.3 and 1.2 ns, respectively. The fact that these times are longer than those of quantum wells indicates that the spin relaxation rate is suppressed in QDs by the increased zero dimensionality. The measurement of tunneling between double QDs which consist of In 0.9Al 0.1As QDs and InAs QDs indicates that the spin relaxation time is not affected by the tunneling process. The spin-polarized carriers were found to tunnel from one dot to another dot while retaining spin polarization.

  18. 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.

  19. Electronic Resource Management and Design

    Science.gov (United States)

    Abrams, Kimberly R.

    2015-01-01

    We have now reached a tipping point at which electronic resources comprise more than half of academic library budgets. Because of the increasing work associated with the ever-increasing number of e-resources, there is a trend to distribute work throughout the library even in the presence of an electronic resources department. In 2013, the author…

  20. 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.

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

    Science.gov (United States)

    Lagoute, Jérôme; Joucken, Frédéric; Repain, Vincent; Tison, Yann; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Sporken, Robert; Conrad, Edward H.; Ducastelle, François; Palsgaard, Mattias; Andersen, Nick Papior; Brandbyge, Mads; Rousset, Sylvie

    2015-03-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000 1 ¯) 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.

  2. Interaction between electrons and tunneling levels in metallic glasses

    International Nuclear Information System (INIS)

    A simple model in which the conduction electrons of a metallic glass experience a local time-dependent potential due to two-level tunneling states is considered. The model exhibits interesting divergent behavior which is quite different from that predicted by an earlier ''s-d Kondo'' model

  3. Inelastic Electron Tunneling Spectroscopy of a Single Nuclear Spin

    Science.gov (United States)

    Delgado, F.; Fernández-Rossier, J.

    2011-08-01

    Detection of a single nuclear spin constitutes an outstanding problem in different fields of physics such as quantum computing or magnetic imaging. Here we show that the energy levels of a single nuclear spin can be measured by means of inelastic electron tunneling spectroscopy (IETS). We consider two different systems, a magnetic adatom probed with scanning tunneling microscopy and a single Bi dopant in a silicon nanotransistor. We find that the hyperfine coupling opens new transport channels which can be resolved at experimentally accessible temperatures. Our simulations evince that IETS yields information about the occupations of the nuclear spin states, paving the way towards transport-detected single nuclear spin resonance.

  4. Solving rate equations for electron tunneling via discrete quantum states

    CERN Document Server

    Bonet, E; Ralph, D C; Bonet, Edgar; Deshmukh, Mandar M.

    2001-01-01

    We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are proportional to temperature. We do this by solving the set of rate equations that can be used to describe electron tunneling via discrete quantum states, for a number of cases important for comparison to experiments, including (1) when just one spin-degenerate level is accessible for transport, (2) when 2 spin-degenerate levels are accessible, with no variation in electron-electron interactions between eigenstates, and (3) when 2 spin-degenerate levels are accessible, but with variations in electron-electron interactions. We also comment on the general case with an arbitrary number of accessible levels. In each case we analyze the voltage-positions, amplitudes,...

  5. Scanning tunnelling microscopy: application to field electron emission studies

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, V.D.; Karabutov, A.V.; Konov, V.I.; Pimenov, S.M.; Prokhorov, A.M. [General Physics Institute, Moscow (Russian Federation)

    1999-04-07

    The principles of scanning tunnelling microscopy (STM) are extended to the study of field electron emission from metal, semiconducting and semi-insulating materials. A specially designed, high-vacuum STM device called a scanning tunnelling field emission microscope (STFEM) is constructed, and new measuring procedures are developed to examine complex physical properties of emission centres. Providing high bias voltages and fast mapping of large squares, the STFEM allows one to obtain reliable statistical data on surface properties, namely topography, emission intensity, surface potential distribution and local electroconductivity. Results from a study of low-field electron emission from CVD diamond films are described to illustrate the functional capabilities of the new STM device. It was found that the diamond films studied are composed of nanograined phases distinguished by their physical properties. It has also been noted that the low-field electron emission from the studied samples is associated with the interfaces of these phases. (author)

  6. Sensitivity of electron temperature measurements with the tunnel probe to a fast electron component

    Science.gov (United States)

    Van Rompuy, T.; Gunn, J. P.; Dejarnac, R.; Stöckel, J.; Van Oost, G.

    2007-05-01

    The tunnel probe is a new kind of Langmuir probe for fast dc measurements of ion flux and electron temperature in the tokamak scrape-off layer. The probe is calibrated using two-dimensional kinetic analysis of the ion current distribution on the concave conductors. Though qualitative agreement with classical Langmuir probe measurements was found, the electron temperature given by the tunnel probe is several times lower. One possible explanation might be an overestimation of the electron temperature by the Langmuir probe, due to a non-Maxwellian electron velocity distribution which can be modelled in a first approach as a two-temperature distribution. Hence the possible influence on the tunnel probe of a small population of nonthermal electrons is investigated by means of the two-dimensional kinetic code XOOPIC. It is found that this influence can be seen as the result of two combined physical effects: nonthermal electrons will reach the back plate (BP) and the ion current distribution over tunnel and the BP will change. The resulting dependence on probe bias and parallel ion current density of the TP sensitivity to nonthermal electrons is not reflected in CASTOR measurement results. Thus nonthermal electrons on their own cannot fully explain the discrepancy between Langmuir and tunnel probe measurements.

  7. Sensitivity of electron temperature measurements with the tunnel probe to a fast electron component

    Energy Technology Data Exchange (ETDEWEB)

    Rompuy, T Van [Department of Applied Physics, Ghent University, Rozier 44, Ghent B-9000 (Belgium); Gunn, J P [Association CEA-EURATOM sur la fusion controlee, Saint Paul Lez Durance F-13108 (France); Dejarnac, R [Institute of Plasma Physics, Association EURATOM-IPP.CR, Za Slovankou 3, 18200 Prague 8 (Czech Republic); Stoeckel, J [Institute of Plasma Physics, Association EURATOM-IPP.CR, Za Slovankou 3, 18200 Prague 8 (Czech Republic); Oost, G Van [Department of Applied Physics, Ghent University, Rozier 44, Ghent B-9000 (Belgium)

    2007-05-15

    The tunnel probe is a new kind of Langmuir probe for fast dc measurements of ion flux and electron temperature in the tokamak scrape-off layer. The probe is calibrated using two-dimensional kinetic analysis of the ion current distribution on the concave conductors. Though qualitative agreement with classical Langmuir probe measurements was found, the electron temperature given by the tunnel probe is several times lower. One possible explanation might be an overestimation of the electron temperature by the Langmuir probe, due to a non-Maxwellian electron velocity distribution which can be modelled in a first approach as a two-temperature distribution. Hence the possible influence on the tunnel probe of a small population of nonthermal electrons is investigated by means of the two-dimensional kinetic code XOOPIC. It is found that this influence can be seen as the result of two combined physical effects: nonthermal electrons will reach the back plate (BP) and the ion current distribution over tunnel and the BP will change. The resulting dependence on probe bias and parallel ion current density of the TP sensitivity to nonthermal electrons is not reflected in CASTOR measurement results. Thus nonthermal electrons on their own cannot fully explain the discrepancy between Langmuir and tunnel probe measurements.

  8. 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.

  9. 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. 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 Kon...

  11. Inelastic electron tunneling spectroscopy of molecular transport junctions

    Energy Technology Data Exchange (ETDEWEB)

    Song, Hyunwook [Kyung Hee University, Yongin (Korea, Republic of); Lee, Takhee [Seoul National University, Seoul (Korea, Republic of); Reed, Mark [Yale University, New Haven, CT (United States)

    2014-05-15

    Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale and molecular junctions. The IETS spectrum provides invaluable information about the structure, bonding, and orientation of component molecules in the junctions. One of the major advantages of IETS is its sensitivity and resolution at the level of single molecules. This review discusses how IETS is used to study molecular transport junctions and presents an overview of recent experimental studies.

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

    OpenAIRE

    Sun, Jie; Li, Ruoyuan; Zhao, Chang; Like YU; 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...

  13. Chiral tunnelling of Dirac electrons in strained graphene

    Science.gov (United States)

    Garcia-Saravia, A.; Cordourier-Maruri, G.; Cifuentes-Quintal, M. E.; Martinez-Guerra, E.; de Coss, R.

    2009-03-01

    The behavior of the electrons in graphene is like massless Dirac fermions, which is a consequence of the characteristic energy spectrum of this material (E˜k). Perfect chiral tunnelling is expected when Dirac electrons pass through a step barrier (Klein paradox). However, in a two-dimensional system like graphene, the perfect tunneling is obtained only in a small range of incident angles. In the present work, we have studied the uniaxial deformation as a method of tunning the electronic transmittance in graphene. The effect of the armchair and zigzag strain on graphene was studied by means of first principles calculations, using the Density Functional Theory. For the calculations we used the pseudopotential-LCAO method. We found that the uniaxial deformations, induce an ellipsoidal distortion of the Dirac cones and isotropy breaking of the Fermi velocity. Finally, we used the Dirac--like equation to find the electronic transmittance as a function of the incident angle. We obtain that the strain induces a strong changes in the transmittance when the deformation is perpendicular to the incident axis.

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

    OpenAIRE

    Hsiao Hsuan Cheng; Yen Chun Lin; Chih Chin Yang

    2012-01-01

    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 favo...

  15. Environmentally Activated Tunneling Events in a Hybrid Single-Electron Box

    OpenAIRE

    Saira, O. -P.; Mottonen, M.; Maisi, V. F.; Pekola, J.P.

    2010-01-01

    We have measured individual tunneling events and Coulomb step shapes in single-electron boxes with opaque superconductor-normal metal tunnel junctions. We observe anomalous broadening of the Coulomb step with decreasing temperature in a manner that is consistent with activation of first-order tunneling events by an external dissipative electromagnetic environment. We demonstrate that the rates for energetically unfavourable tunneling events saturate to finite values at low t...

  16. Electron-beam-assisted scanning tunneling microscopy of insulating surfaces

    Science.gov (United States)

    Bullock, Eugene Thomas

    2000-07-01

    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 yields, the population of conduction band states could be quite significant. Second, for specific incident primary beam energies, the resulting electron yield will be equal to the incoming beam intensity. These are referred to as the cross over energies (E1 and E2). For a stationary primary beam at E2 the current entering the sample and the current leaving sample are equal so that a state of dynamic equilibrium is quickly reached whereby the charge density distribution local to primary beam, both at the surface and within the material, is fixed. Thus, if the surface of an insulator is illuminated with an energetic electron beam at E2, the surface will be locked to some potential and there will be filled conduction band states. Under these conditions, it may be possible to make STM measurements of material even though it is insulating. That is, from an STM point of view, it may be possible to make an insulator `act' like a conductor. In order to test the principle of e-BASTM, metals, thin insulating films, and bulk insulators have been examined. For metals, as expected, we observe no alteration of the tunneling signal due to the PE beam. However, with SiO 2, there is a significant increase in the tunneling current which can be directly attributed to the PE beam. For Al2O3 and CaF2 it is found that the surfaces are damaged too quickly by the PE beam for this technique to be applied suggesting that e-BASTM may only be suitable for a small class of materials. The STM (not e-BASTM) has been used to electrically stress thin films of SiO2 (native oxide thickness). The stressing is observed to create trapping states which have been connected to stress induced leakage currents (SILC) in metal/SiO2/Si devices. The effect of the stress is observed to depend on the polarization of the applied bias (positive or negative). The trapping site density is observed to reach levels on the order of 1013-1014 traps/cm2 which is about a factor of 10-100 higher than what has been previously been reported.

  17. Enhancement of Radiative Plasmon Decay by Hot Electron Tunneling.

    Science.gov (United States)

    Wang, Xiao; Braun, Kai; Zhang, Dai; Peisert, Heiko; Adler, Hilmar; Chassé, Thomas; Meixner, Alfred J

    2015-08-25

    Here we demonstrate that photon emission induced by inelastic tunneling through a nanometer single gap between a sharp Au tip and an Au substrate can be significantly enhanced by the illumination of the junction with 634 nm laser light with an electric field component oriented parallel to the tip-axis, i.e., perpendicular to the sample. Analyzing photoluminescence (PL) spectra recorded as a function of bias voltage allows us to distinguish between PL from (1) the decay of electron-hole pairs created by the laser excited sp/d interband transition with a characteristic band at 690 nm and (2) the red-shifted radiative decay of characteristic plasmon modes formed by the gap. Since the electroluminescence spectra (without laser) already show the plasmonic gap modes, we conclude that the enhanced intensity induced by laser illumination originates from the radiative decay of hot electrons closely above the Fermi level via inelastic tunneling and photon emission into the plasmon modes. Since these processes can be independently controlled by laser illumination and the amplitude of the bias voltage, it is of great interest for designing new switchable photon emission plasmonic devices. PMID:26200215

  18. Tunneling electron induced luminescence from porphyrin molecules on monolayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Geng, Feng; Kuang, Yanmin; Yu, Yunjie; Liao, Yuan; Zhang, Yao; Zhang, Yang; Dong, Zhenchao, E-mail: zcdong@ustc.edu.cn

    2015-01-15

    Using epitaxially grown graphene on Ru(0001) as a decoupling layer, we investigate the evolution of tunneling electron induced luminescence from different number of layers of porphyrin molecules. Light emission spectra and photon maps, acquired via a combined optical setup with scanning tunneling microscopy (STM), indicate that the electronic decoupling effect of a monolayer (ML) graphene alone is still insufficient for generating molecule-specific emission from both the 1st- and 2nd-layer porphyrin molecules. Nevertheless, interestingly, the plasmonic emission is enhanced for the 1st-layer but suppressed for the 2nd-layer in comparison with the plasmonic emission on the monolayer graphene. Intrinsic intramolecular molecular fluorescence occurs at the 3rd-layer porphyrin. Such molecular thickness is about two MLs thinner than previous reports where molecules were adsorbed directly on metals. These observations suggest that the monolayer graphene does weaken the interaction between molecule and metal substrate and contribute to the reduction of nonradiative decay rates. - Highlights: • Showing molecularly resolved photon maps of graphene and porphyrins on it. • Revealing the influence of spacer thickness on molecular electroluminescence. • Graphene does weaken the interaction between molecules and metal substrate.

  19. Metallic single-electron transistor without traditional tunnel barriers

    Energy Technology Data Exchange (ETDEWEB)

    Krupenin, V A; Savvateev, M N [Laboratory of Cryoelectronics, Moscow State University, Vorob' evy gory, 119899 Moscow (Russian Federation); Zorin, A B; Presnov, D E [Institute of Nuclear Physics, Moscow State University, Vorob' evy gory, 119899 Moscow (Russian Federation); Niemeyer, J [Physikalisch-Technische Bundesanstalt, 38116 Braunschweig (Germany)

    2001-10-01

    We report a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips ({approx} 1 {mu}m long) connecting a 1 {mu}m-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 k{omega} showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages Vg. In the Coulomb blockade region (|V| {<=} about 0.5 mV), we observed a strong suppression of the co-tunneling current allowing appreciable modulation curves V(Vg) to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlO{sub x}/Al single-electron transistors, viz. {delta}Q {approx} 5 x 10{sup -4}e/{radical}Hz at 10 Hz. (5. superconductor-metal-insulator transitions)

  20. Tunneling electron induced luminescence from porphyrin molecules on monolayer graphene

    International Nuclear Information System (INIS)

    Using epitaxially grown graphene on Ru(0001) as a decoupling layer, we investigate the evolution of tunneling electron induced luminescence from different number of layers of porphyrin molecules. Light emission spectra and photon maps, acquired via a combined optical setup with scanning tunneling microscopy (STM), indicate that the electronic decoupling effect of a monolayer (ML) graphene alone is still insufficient for generating molecule-specific emission from both the 1st- and 2nd-layer porphyrin molecules. Nevertheless, interestingly, the plasmonic emission is enhanced for the 1st-layer but suppressed for the 2nd-layer in comparison with the plasmonic emission on the monolayer graphene. Intrinsic intramolecular molecular fluorescence occurs at the 3rd-layer porphyrin. Such molecular thickness is about two MLs thinner than previous reports where molecules were adsorbed directly on metals. These observations suggest that the monolayer graphene does weaken the interaction between molecule and metal substrate and contribute to the reduction of nonradiative decay rates. - Highlights: • Showing molecularly resolved photon maps of graphene and porphyrins on it. • Revealing the influence of spacer thickness on molecular electroluminescence. • Graphene does weaken the interaction between molecules and metal substrate

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

    Energy Technology Data Exchange (ETDEWEB)

    Elesin, V. F., E-mail: VFElesin@mephi.ru [National Research Nuclear University MEPhI (Russian Federation)

    2013-11-15

    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.

  2. Metallic single-electron transistor without traditional tunnel barriers

    CERN Document Server

    Krupenin, V A; Presnov, D E; Savvateev, M N; Niemeyer, J C

    2000-01-01

    We report on a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips (~ 1um long) connecting a 1 um-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 kOhm showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages V_g. In the Coulomb blockade region (|V| < 0.5 mV), we observed a strong suppression of the cotunneling current allowing appreciable modulation curves V-V_g to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlOx/Al single-electron transistors.

  3. Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope

    OpenAIRE

    Wu, Shiwei; Ho, Wilson

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

  4. 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.

  5. 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.

  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. On the Dynamics of Single-Electron Tunneling in Semiconductor Quantum Dots under Microwave Radiation

    OpenAIRE

    Qin, Hua

    2001-01-01

    Efforts are made in this thesis to reveal the dynamics of single-electron tunneling and to realize quantum bits (qubits) in semiconductor quantum dots. At low temperatures, confined single quantum dots and double quantum dots are realized in the twodimensional electron gas (2DEG) of AlGaAs/GaAs heterostructures. For transport studies, quantum dots are coupled to the drain and source contacts via tunnel barriers. Electron-electron interaction in such closed quantum dots leads to...

  9. Electron tunneling at Al-SiO2 interfaces

    Science.gov (United States)

    Av-Ron, M.; Shatzkes, M.; DiStefano, T. H.; Gdula, R. A.

    1981-04-01

    The Murphy-Good tunneling theory, modified with a Franz-type two-band dispersion relation, accurately represents emission of electrons from metals into SiO2 using parameters that are invariant with temperature and that agree with independent measurements. Parameters related to properties of the SiO2 do not change when different metal electrodes are used. Deviations of the measured I-V characteristic from the model calculation which occur at low field can be explained in terms of interfacial inhomogeneities in the effective barrier height. For thin dry SiO2 grown on boron-dope silicon, the effective size of the inhomogeneities increases with decreasing oxidation temperature.

  10. Student attitudes towards electronic information resources

    OpenAIRE

    Kathryn Ray; Joan Day

    1998-01-01

    Students are increasingly expected to use electronic resources while at university. Studies were undertaken to determine the level of use of this type of resource, how students feel about various issues surrounding electronic resources and whether attitudes change dependent upon subject studied. 317 students across three universities completed questionnaires to determine level of use of various electronic information resources; ways in which they felt electronic resources had hindered or impr...

  11. Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy.

    Science.gov (United States)

    Artés, Juan M; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

    2011-03-22

    We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current?distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (?) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains. PMID:21539019

  12. Shapes of leading tunnelling trajectories for single-electron molecular ionization

    CERN Document Server

    Bondar, Denys I; Ivanov, Misha Yu

    2010-01-01

    Based on the geometrical approach to tunnelling by P.D. Hislop and I.M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Aref, T.; Averin, A.; Nguyend, H. Q.; Pekola, J. P. [Low Temperature Laboratory (OVLL), Aalto University School of Science, P.O. Box 13500, 00076 Aalto (Finland); Dijken, S. van; Yao, L. D. [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Ferring, A. [Kirchhoff-Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, D-69120 Heidelberg (Germany); Koberidze, M.; Nieminen, R. M. [COMP/Department of Applied Physics, Aalto University School of Science, P.O. Box 11100, FI-00076 Aalto, Espoo (Finland); Maisi, V. F., E-mail: ville.maisi@gmail.com [Low Temperature Laboratory (OVLL), Aalto University School of Science, P.O. Box 13500, 00076 Aalto (Finland); Centre for Metrology and Accreditation (MIKES), P.O. Box 9, 02151 Espoo (Finland)

    2014-08-21

    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.

  14. 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...

  15. Measurement of Counting Statistics of Electron Transport in a Tunnel Junction

    OpenAIRE

    Bomze, Yu.; Gershon, G.; Shovkun, D.; Levitov, L S; Reznikov, M.

    2005-01-01

    We present measurements of the time-dependent fluctuations in electrical current in a voltage-biased tunnel junction. We were able to simultaneously extract the first three moments of the tunnel current counting statistics. Detailed comparison of the second and the third moment reveals that counting statistics is accurately described by the Poissonian distribution expected for spontaneous current fluctuations due to electron charge discreteness, realized in tunneling transpo...

  16. Electronic Resources: A Wolf in Sheep's Clothing?

    Science.gov (United States)

    Schaffner, Bradley L.

    2001-01-01

    Examines the impact of electronic technology on libraries and scholarship. Focuses on some of the challenges of using electronic resources in research libraries, which include cost of acquiring electronic formats and the effect such expenditures have on other library services and collection development practices. Explores how electronic resources

  17. Wrangling Electronic Resources: A Few Good Tools

    OpenAIRE

    Brandy Klug

    2010-01-01

    There are several freely available tools today that fill the needs of librarians tasked with maintaining electronic resources, that assist with tasks such as editing MARC records and maintaining web sites that contain links to electronic resources. This article gives a tour of a few tools the author has found invaluable as an Electronic Resources Librarian.

  18. Electron and phonon Cooling in a Superconductor - Normal Metal - Superconductor Tunnel Junction

    OpenAIRE

    Rajauria, Sukumar; Luo, P. S.; Fournier, T.; Hekking, F. W. J.; Courtois, H; Pannetier, B.

    2006-01-01

    We present evidence for the cooling of normal metal phonons by electron tunneling in a Superconductor - Normal metal - Superconductor tunnel junction. The normal metal electron temperature is extracted by comparing the device current-voltage characteristics to the theoretical prediction. We use a quantitative model for the phonon cooling that includes the electron-phonon coupling in the normal metal and the Kapitza resistance between the substrate and the metal. It gives an ...

  19. Rates, distances, and energy control of electron tunneling reactions in rigid media

    International Nuclear Information System (INIS)

    Electron tunneling leads to transfer of trapped positive, or negative charge tens of angstroms in rigid matrices. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and adds sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as in radiation chemistry. We feel that the question of hopping vs. tunneling is definitely settled in favor of tunneling for intermolecular electron transfer at low temperatures. Hopping cannot yet be conclusively ruled out in reactions of trapped electrons. Hopping is expected to become important in many media near room temperature

  20. Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles

    CERN Document Server

    Xue, Y; Xue, Yongqiang; Ratner, Mark A.

    2004-01-01

    We present a microscopic study of single-electron tunneling in nanomechanical double-barrier tunneling junctions formed using a vibrating scanning nanoprobe and a metallic nanoparticle connected to a metallic substrate through a molecular bridge. We analyze the motion of single electrons on and off the nanoparticle through the tunneling current, the displacement current and the charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate the mechanical single-electron turnstile effect by applying the theory to a gold nanoparticle connected to the gold substrate through alkane dithiol molecular bridge and probed by a vibrating platinum tip.

  1. The use of MIM tunnel junctions to investigate kinetic electron excitation in atomic collision cascades

    International Nuclear Information System (INIS)

    A novel technique is introduced to investigate the kinetic excitation of electrons in a solid by bombardment with energetic ions. The sample is prepared as a metal-insulator-metal (MIM) tunnel junction which opens the possibility to detect hot electrons with excitation energies well below the vacuum barrier. The excitations produced by the projectile impact onto the top electrode are detected as a tunnel current into the underlying base electrode. By varying the top electrode thickness, the elastic transport of hot electrons towards the tunnel junction can be studied

  2. Rates, distances, and energy control of electron tunneling reactions in rigid media

    International Nuclear Information System (INIS)

    Electron tunneling leads to the transfer of trapped positive or negative charges by tens of angstrom in rigid matrices. Electron tunneling reactions occur after the radiolysis of a rigid inert matrix containing two added solutes. The ''initial'' species, the matrix, trapped electrons and trapped positive charges of ''holes'', can each react with either solute, and both negative and positive charges can be transferred from one solute to another. These reactions occur by long range tunneling. Trapped electrons can react with radiation-produced free radicals, and ion recombination can occur between all possible pairs of + and - species. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and add sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as radiation chemistry. Hopping versus tunneling seemed to be settled in favor of tunneling for intermolecular electron transfer at low temperature. Hopping is expected to become important in many media near room temperature, and thus cannot be conclusively ruled out in the reactions of trapped electrons. The tunneling effect in liquids is usually small, leading only to the increase of a few angstrom in reaction radius in low viscosity liquids, but tunneling effects can be quite important in overcoming steric hindrance or Coulomb repulsion. (Yamashita, S.)

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

    CERN Document Server

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

    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 that require taking into account electron interactions and relaxation.

  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. Measurement of electron temperature fluctuations with tunnel probe in the CASTOR tokamak

    International Nuclear Information System (INIS)

    The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. Two-dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for making fast de measurements of ion flux and electron temperature. Qualitative agreement with classical Langmuir probe measurements is found, but the electron temperature given by the tunnel probe is several times lower. This discrepancy can be caused by secondary electron emission, or the presence of suprathermal electrons. Strong reduction of ion flux and electron temperature fluctuations is observed during electrode biasing. (orig.)

  6. Measurement of electron temperature fluctuations with tunnel probe in the CASTOR tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Gunn, J.P. [Association EURATOM-CEA sur la fusion controlee, Saint Paul Lez Durance (France); Stoeckel, J.; Adamek, J.; Duran, I.; Hron, M.; Panek, R.; Zacek, F. [Inst. of Plasma Physics, Association EURATOM-IPP.CR, Prague (Czech Republic); Van Rompuy, T.; De Beule, P.; Van Oost, G. [Dept. of Applied Physics, Ghent Univ. (Belgium); Balan, P.; Schrittwieser, R. [Inst. for Ion Physics, Univ. of Innsbruck (Austria); Barina, O.; Hrach, R.; Vicher, M. [Charles Univ. in Prague, Faculty of Mathematics and Physics (Czech Republic)

    2004-07-01

    The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. Two-dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for making fast de measurements of ion flux and electron temperature. Qualitative agreement with classical Langmuir probe measurements is found, but the electron temperature given by the tunnel probe is several times lower. This discrepancy can be caused by secondary electron emission, or the presence of suprathermal electrons. Strong reduction of ion flux and electron temperature fluctuations is observed during electrode biasing. (orig.)

  7. Atomic scale imaging and spectroscopy of individual electron trap states using force detected dynamic tunnelling.

    Science.gov (United States)

    Johnson, J P; Zheng, N; Williams, C C

    2009-02-01

    We report the first atomic scale imaging and spectroscopic measurements of electron trap states in completely non-conducting surfaces by dynamic tunnelling force microscopy/spectroscopy. Single electrons are dynamically shuttled to/from individual states in thick films of hafnium silicate and silicon dioxide. The new method opens up surfaces that are inaccessible to the scanning tunnelling microscope for imaging and spectroscopy on an atomic scale. PMID:19417360

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

    OpenAIRE

    Hollstein, Maximilian; Pfannkuche, Daniela

    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 ...

  9. Probing the Longitudinal Momentum Spread of the Electron Wave Packet at the Tunnel Exit

    OpenAIRE

    Madsen Lars B.; Smolarski Mathias; Dimitrovski Darko; Pfeiffer Adrian N.; Landsman Alexandra S.; Cirelli Claudio; Keller Ursula

    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 comb...

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

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-Environmental and Forest Biology, CNR, I-05010 Porano (Italy); Kumar, Vivek; Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

    2015-05-04

    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.

  11. Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors

    Science.gov (United States)

    Vaziri, S.; Belete, M.; Dentoni Litta, E.; Smith, A. D.; Lupina, G.; Lemme, M. C.; Östling, M.

    2015-07-01

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the 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 electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 103 A cm-2 (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

  12. Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors.

    Science.gov (United States)

    Vaziri, S; Belete, M; Dentoni Litta, E; Smith, A D; Lupina, G; Lemme, M C; Östling, M

    2015-08-14

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the 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 electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 10(3) A cm(-2) (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices. PMID:26176739

  13. When does an electron exit a tunneling barrier?

    OpenAIRE

    Ivanov M. Yu.; Smirnova O.; Patchkovskii S.; Mairesse Y.; Dagan M.; Bruner B. D.; Soifer H.; Shafir D.; Dudovich N.

    2013-01-01

    We probe the dynamics of tunnel ionization via high harmonic generation. We characterize the ionization dynamics in helium atoms, and apply our approach to resolve subtle differences in ionization from different orbitals of a CO2 molecule.

  14. When does an electron exit a tunneling barrier?

    Directory of Open Access Journals (Sweden)

    Ivanov M. Yu.

    2013-03-01

    Full Text Available We probe the dynamics of tunnel ionization via high harmonic generation. We characterize the ionization dynamics in helium atoms, and apply our approach to resolve subtle differences in ionization from different orbitals of a CO2 molecule.

  15. Ultralarge area MOS tunnel devices for electron emission

    DEFF Research Database (Denmark)

    Thomsen, Lasse BjØrchmar; Nielsen, Gunver

    2007-01-01

    A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxide) MOS capacitors have been fabricated to investigate their functionality and the variations in oxide thickness, with the use as future electron emission devices as the goal. I-V characteristics show very low leakage current and excellent agreement to the Fowler-Nordheim expression for the current density. Oxide thicknesses have been extracted by fitting a model based on Fermi-Dirac statistics to the C-V characteristics. By plotting I-V characteristics in a Fowler plot, a measure of the thickness of the oxide can be extracted from the tunnel current. These apparent thicknesses show a high degree of correlation to thicknesses extracted from C-V characteristics on the same MOS capacitors, but are systematically lower invalue. This offset between the thicknesses obtained by C-V characteristics and I-V characteristics is explained by an inherent variation of the oxide thickness. Comparison of MOS capacitors with different oxide areas ranging from 1 cm(2) to 10 mu m(2), using the slope from Fowler-Nordheim plots of the I-V characteristics as a measure of the oxide thickness, points toward two length scales of oxide thickness variations being similar to 1 cm and similar to 10 mu m, respectively.

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

    OpenAIRE

    O.Ya. Farenyuk; A.M. Shvaika

    2006-01-01

    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 all...

  17. 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.

  18. 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.

  19. Negative differential resistance in GaN tunneling hot electron transistors

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Zhichao; Nath, Digbijoy; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43202 (United States)

    2014-11-17

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport.

  20. Negative differential resistance in GaN tunneling hot electron transistors

    International Nuclear Information System (INIS)

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport

  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. 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…

  3. Coherent oscillations of electrons in tunnel-coupled wells under ultrafast intersubband excitation

    International Nuclear Information System (INIS)

    Ultrafast intersubband excitation of electrons in tunnel-coupled wells is studied in respect of its dependence on the structure parameters, the duration of the infrared pump and the detuning frequency. The temporal dependences of the photoinduced carrier concentration and dipole moment are obtained for two cases of transitions: from the single ground state to the tunnel-coupled excited states and from the tunnel-coupled states to the single excited state. The peculiarities of dephasing and population relaxation processes are also taken into account. The nonlinear regime of the response is also considered when the splitting energy between the tunnel-coupled levels is renormalized by the photoexcited electron concentration. The dependences of the period and the amplitude of oscillations on the excitation pulse are presented with a description of the damping of the nonlinear oscillations

  4. Photon induced tunneling of electron through a graphene electrostatic barrier

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, R. [Department of Physics, P.K. College, Contai, Purba Medinipur, West Bengal 721401 (India); Sinha, C. [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2013-11-14

    The influence of an external intense laser field on the tunneling transport (ballistic) of the Dirac fermions through a monolayer graphene electrostatic barrier is studied in the framework of the Floquet approach for a continuous wave, linearly polarized, monochromatic laser. The Klein tunneling is shown to be suppressed by the irradiation of a strong laser field, arising due to breaking of chiral symmetry. The symmetric nature of the field free angular transmission spectrum around the normal to the well-barrier interface is destroyed due to the additional coupling between the pseudo-spin and the time dependent vector potential. The energy distribution of the tunneling spectrum displays Fano resonance which is absent for a laser assisted conventional electrostatic barrier but similar to the case of quantum well structures, providing an optical tool to identify field free quasi bound states inside the graphene nanostructures.

  5. Nonconstant electronic density of states tunneling inversion for A15 superconductors: Nb3Sn

    OpenAIRE

    Freericks, J. K.; Liu, A. Y.; Quandt, A.; Geerk, J.

    2002-01-01

    We re-examine the tunneling data on A15 superconductors by performing a generalized McMillan-Rowell tunneling inversion that incorporates a nonconstant electronic density of states obtained from band-structure calculations. For Nb3Sn, we find that the fit to the experimental data can be slightly improved by taking into account the sharp structure in the density of states, but it is likely that such an analysis alone is not enough to completely explain the superconducting tun...

  6. The Wigner time delay for laser induced tunnel-ionization via the electron propagator

    OpenAIRE

    Yakaboylu, Enderalp; Klaiber, Michael; Hatsagortsyan, Karen Z.

    2014-01-01

    Recent attoclock experiments using the attsecond angular streaking technique enabled the measurement of the tunneling time delay during laser induced strong field ionization. Theoretically the tunneling time delay is commonly modelled by the Wigner time delay concept which is derived from the derivative of the electron wave function phase with respect to energy. Here, we present an alternative method for the calculation of the Wigner time delay by using the fixed energy prop...

  7. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  8. 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.

  9. 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 astronomical growth of e-resources—e-journals, e-books, online databases and so on; libraries spend phenomenally on acquisition 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 view of various projects initiated for archiving digital content of scholarly journals.

  10. 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.

  11. Imaging surfaces with reflected electrons from a field emission scanning tunnelling microscope: image contrast mechanisms

    International Nuclear Information System (INIS)

    Electrons backscattered from a scanning tunnelling microscope operating in the field emission mode have been collected to produce images of a rough Si(111) surface. We have obtained a spatial resolution of about 40 nm in such images. Comparison between backscattered electron images and topographic images reveals that edge enhancement and shadowing are important contrast mechanisms. (author)

  12. 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 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

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

    OpenAIRE

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

    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...

  14. Electron tunneling pathways and role of adenine in repair of cyclobutane pyrimidine dimer by DNA photolyase.

    Science.gov (United States)

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

    2012-05-16

    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 photoinitiated 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 reactants, all intermediates and final products, and determined their reaction time scales. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repair and for the final electron return to restore the active cofactor and complete the catalytic photocycle. Significantly, we found that the adenine moiety of the unusual bent flavin cofactor is essential to mediating all electron-transfer dynamics through a superexchange mechanism, leading to a delicate balance of time scales. The cyclobutane ring splitting takes tens of picoseconds, while electron-transfer dynamics all occur on a longer time scale. The active-site structural integrity, unique electron tunneling pathways, and the critical role of adenine ensure the synergy of these elementary steps in this complex photorepair machinery to achieve maximum repair efficiency which is close to unity. Finally, we used the Marcus electron-transfer theory to evaluate all three electron-transfer processes and thus obtained their reaction driving forces (free energies), reorganization energies, and electronic coupling constants, concluding that the forward and futile back-electron transfer is in the normal region and that the final electron return of the catalytic cycle is in the inverted region. PMID:22533849

  15. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach.

    Science.gov (United States)

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-01-01

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport. PMID:26596778

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

    Science.gov (United States)

    Hege, Hans-Christian; Manz, Jörn; Marquardt, Falko; Paulus, Beate; Schild, Axel

    2010-11-01

    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.

  17. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    Science.gov (United States)

    Wang, R.; Williams, C. C.

    2015-09-01

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  18. Rates, distances, and energy control of electron tunneling reactions in rigid media

    Energy Technology Data Exchange (ETDEWEB)

    Miller, John R.; Beitz, James V.

    1979-01-01

    Electron tunneling leads to transfer of trapped positive, or negative charge tens of angstroms in rigid matrices. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and adds sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as in radiation chemistry. We feel that the question of hopping vs. tunneling is definitely settled in favor of tunneling for intermolecular electron transfer at low temperatures. Hopping cannot yet be conclusively ruled out in reactions of trapped electrons. Hopping is expected to become important in many media near room temperature (T approx. less than 200/sup 0/K).

  19. Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study

    CERN Document Server

    Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco

    2015-01-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...

  20. 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

  1. Transient localized electron dynamics simulation during femtosecond laser tunnel ionization of diamond

    International Nuclear Information System (INIS)

    Highlights: ? A first-principles calculation of nonlinear electron–photon interactions when tunnel ionization dominates is presented. ? TDDFT is applied for the description of transient localized electrons dynamics. ? The relationships among average absorbed energy, Keldysh parameter and laser intensity are revealed. -- Abstract: A real-time and real-space time-dependent density-functional theory (TDDFT) is applied to simulate the nonlinear electron–photon interactions during femtosecond laser processing of diamond when tunnel ionization dominates. The transient localized electron dynamics including the electron excitation, energy absorption and electron density evolution are described in this Letter. In addition, the relationships among average absorbed energy, Keldysh parameter and laser intensity are revealed when the laser frequency is fixed.

  2. Highly Efficient Midinfrared On-Chip Electrical Generation of Graphene Plasmons by Inelastic Electron Tunneling Excitation

    CERN Document Server

    Ooi, Kelvin J A; Hsieh, Chang Yu; Tan, Dawn T H; Ang, Lay Kee

    2015-01-01

    Inelastic electron tunneling provides a low-energy pathway for the excitation of surface plasmons and light emission. We theoretically investigate tunnel junctions based on metals and graphene. We show that graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the midinfrared wavelength regime. Compared to gold and silver, the enhancement can be up to 10 times for similar wavelengths and up to 5 orders at their respective plasmon operating wavelengths. Tunneling excitation of graphene plasmons promises an efficient technology for on-chip electrical generation and manipulation of plasmons for graphene-based optoelectronics and nanophotonic integrated circuits.

  3. Electron beam damage of chemisorbed surface species: a tunneling spectroscopy study

    International Nuclear Information System (INIS)

    Electron beam damage is a problem for low-energy electron diffraction, Auger electron spectroscopy, and electron microscopy. Tunneling spectroscopy has been used to study the damage caused by 30 keV incident electrons on chemisorbed monolayer films of hexanoic acid, 2,4-hexadienoic acid, and benzoic acid. The results on monolayer films are compared to existing work on bulk samples. Damage cross sections are similar to bulk values; molecules with more delocalized electrons are more resistant to damage. In contrast to bulk results, however, little if any conjugation or cross linking is found after irradiation. (Auth.)

  4. 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.

  5. Energy and Effective Mass Dependence of Electron Tunnelling Through Multiple Quantum barriers in Different Heterostructures

    OpenAIRE

    Gain, Jatindranath; Sarkar, Madhumita Das; Kundu, Sudakshina

    2010-01-01

    Tunneling of electrons through the barriers in heterostructures has been studied, within unified transfer matrix approach. The effect of barrier width on the transmission coefficient of the electrons has been investigated for different pairs of semi conducting materials that are gaining much importance recently. These pairs include CdS/CdSe, AlGaAs/GaAs and InAs/AlSb. Barrier dimensions have been reduced from 20nm to 5nm to observe the effect of scaling on tunneling properti...

  6. Phase change of tetrahedral amorphous-carbon by low energy electrons in a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Low energy electron-based energy deposition in tetrahedral amorphous-carbon thin films by a scanning tunnelling microscope leads to a local phase change of the carbon. Both the mass density and the electrical resistivity are reduced indicating a graphitization. We expose nano-sized surface areas to field emitted low energy electrons under high vacuum conditions and investigate the temperature and electron energy dependence of the carbon phase change process. Supplementary topography measurements are performed by atomic force microscopy.

  7. 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 ...

  8. 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.

  9. Energy and Effective Mass Dependence of Electron Tunnelling Through Multiple Quantum barriers in Different Heterostructures

    CERN Document Server

    Gain, Jatindranath; Kundu, Sudakshina

    2010-01-01

    Tunneling of electrons through the barriers in heterostructures has been studied, within unified transfer matrix approach. The effect of barrier width on the transmission coefficient of the electrons has been investigated for different pairs of semi conducting materials that are gaining much importance recently. These pairs include CdS/CdSe, AlGaAs/GaAs and InAs/AlSb. Barrier dimensions have been reduced from 20nm to 5nm to observe the effect of scaling on tunneling properties. Material depended is highlighted for electrons with energy varying from below the barrier height to above it. The electron effective mass inside the barrier and the well are often different. The results show that the coupling effect leads to significant changes on the transmission effect. . The effective-mass dependant transmission coefficient has been plotted with respect to electron energy. The computation is based on the transfer matrix method by using MATLAB.

  10. 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.

  11. Surface morphology and transport properties of Cr nanoparticles in single electron tunneling regime

    Energy Technology Data Exchange (ETDEWEB)

    Koda, Tetsunori; Mizuguchi, Masaki; Takanashi, Koki [Institute for Materials Research, Tohoku University, Sendai, 980-8577 (Japan); Mitani, Seiji, E-mail: koda@imr.tohoku.ac.jp [National Institute for Materials Science, Tsukuba, 305-0047 (Japan)

    2011-01-01

    We have carried out an investigation of surface structures of Cr nanoparticles grown on a MgO layer for studying single electron tunneling (SET). Reflection high-energy electron diffraction pattern changes from spotty to streak with decreasing Cr nominal thickness, while Cr forms nano size particles with the size of around 3.5 nm in diameter for all the samples. The double tunnel junctions for the Cr nominal thickness of 0.1 nm show clear Coulomb blockade with the threshold voltage of 50 mV, indicating that this Cr nanoparticle satisfies the condition for the appearance of SET. The relatively large volume of the Cr nanoparticles may be related with the fact that tunnel magnetoresistance due to spin accumulation in Cr nanoparticles is small.

  12. Resonant tunneling of electrons in asymmetric double quantum wells under crossed electric and magnetic fields

    International Nuclear Information System (INIS)

    It has been investigated the influence of an uniform electric field, applied in the growth direction, and an uniform magnetic field, perpendicular to this direction, on the resonant tunneling of electrons in a system formed by two asymmetric quantum wells separated by a thin barrier. The semiconductor heterostructure is considered in the effective mass approximation and one band model. The method we have used to calculated the electronic structure is based on the solution of the time-dependent Schroedinger equation using the split-operator technique. The tunneling dynamics in the resonance condition is studied using the time evolution of a wave-packet from which we determine the tunneling time. A comparison with recent experimental data is presented. (author). 10 refs., 4 figs

  13. 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.

  14. 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.

  15. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-11-03

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution.

  16. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution

  17. Electron Tunneling Pathway and Role of Adenine in Repair of Damaged DNA by Photolyase

    Science.gov (United States)

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

    2012-06-01

    Through electron tunneling, photolyase, a photoenzyme, restores damaged DNA into normal bases. Here, we report our systematic characterization and analyses of three electron transfer processes in thymine dimer restoration by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. We observed the complete dynamics of the reactants, all intermediates and final products, and determined their reaction time scales. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repairing and for the final electron return to restore the active cofactor and complete the repair photocycle. Significantly, we found that the adenine moiety of the unusual bent cofactor is essential to mediating all electron transfer dynamics through a super-exchange mechanism, leading to a delicate balance of time scales. The active-site structural integrity, unique electron tunneling pathways and the critical role of adenine assure these elementary dynamics in synergy in this complex photorepair machinery to achieve the maximum repair efficiency close to unity. Z. Liu, C. Tan, X. Guo, Y.-T. Kao, J. Li, L. Wang, A. Sancar, and D. Zhong, Proc. Natl. Acad. Sci. USA 108, 14831 (2011) J. Li, Z. Liu, C. Tan, X. Guo, L. Wang, A. Sancar, and D. Zhong, Nature 466, 887 (2010)

  18. Dynamics and pathway of electron tunneling in repair of damaged DNA by photolyase

    Science.gov (United States)

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

    2013-03-01

    Through electron tunneling, photolyase, a photoenzyme, restores damaged DNA into normal bases. Here, we report our systematic characterization and analyses of three electron transfer processes in thymine dimer restoration by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repairing and for the final electron return to restore the active cofactor and complete the repair photocycle. Significantly, we found that the adenine moiety of the unusual bent cofactor is essential to mediating all electron-transfer dynamics through a super-exchange mechanism, leading to a delicate balance of time scales. The active-site structural integrity, unique electron tunneling pathways and the critical role of adenine assure these elementary dynamics in synergy in this complex photorepair machinery to achieve the maximum repair efficiency close to unity. The authors thank Drs. Chaitanya Sexana, Yi Yang, and Chen Zang for the initial help with experiment, and Prof. Sherwin Singer and Dr. Ali Hassanali for discussion.

  19. 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 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)

  20. 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.

  1. Spin Accumulation Encoded in Electronic Noise for Mesoscopic Billiards with Finite Tunneling Rates

    OpenAIRE

    Ramos, J. G. G. S.; Barbosa, A. L. R.; Bazeia, D.; Hussein, M. S

    2011-01-01

    We study the effects of spin accumulation (inside reservoirs) on electronic transport with tunneling and reflections at the gates of a quantum dot. Within the stub model, the calculation focus on the current-current correlation function for the flux of electrons injected into the quantum dot. The linear response theory used allows to obtain the noise power in the regime of thermal crossover as a function of parameters that reveal the spin polarization at the reservoirs. The ...

  2. DNA - Nanoelectronics Realization of a Single Electron Tunneling Transistor and a Quantum Bit Element

    CERN Document Server

    Ben-Jacob, E; Caspi, S; Ben-Jacob, Eshel; Hermon, Ziv; Caspi, Shay

    1998-01-01

    Based on the understanding that chemical bonds can act as tunnel junctions in the Coulomb blockade regime, and on the technical ability to coat a DNA strand with metal, we suggest that DNA can be used to built logical devices. We discuss two explicit examples: a Single Electron Tunneling Transistor (SET) and a Quantum Bit Element. These devices would be literally in the nano-meter scale and would be able to operate at room temperature. In addition they would be identical to each other, highly stable and would have a self assembly property.

  3. Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions

    Energy Technology Data Exchange (ETDEWEB)

    Huddleston, R.K.; Miller, J.R.

    1982-04-15

    A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 77/sup 0/K. Good agreement between the model and the experimental kinetic results was obtained.

  4. Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions

    International Nuclear Information System (INIS)

    A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 770K. Good agreement between the model and the experimental kinetic results was obtained

  5. Electronic transport in graphene/CdSe nanoparticle monolayer/graphene tunneling devices

    Science.gov (United States)

    Zhang, Datong; Lu, Chenguang; van der Zande, Arend; Kim, Philip; Herman, Irving P.

    2015-03-01

    We fabricated graphene/CdSe nanoparticle monolayer/graphene sandwich device structures. The CdSe nanoparticle monolayer is formed on a liquid-air surface before transferring it onto the bottom graphene layer that had been micro-exfoliated onto a 285 nm SiO2/Si substrate. The top graphene layer is transferred to the targeted area on the CdSe nanoparticle monolayer via a dry transfer technique. Tunneling-type vertical transport is observed, which is fitted by tunneling models that suggest that ligand shell instead of nanoparticle core is the major barrier of tunneling. Photoconductivity is enhanced but with low exciton separation efficiency when the laser is on the junction area, also suggesting that ligand shell is the major barrier of electronic transport in the sandwich structure.

  6. Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons.

    Science.gov (United States)

    Natterer, Fabian D; Zhao, Yue; Wyrick, Jonathan; Chan, Yang-Hao; Ruan, Wen-Ying; Chou, Mei-Yin; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B; Stroscio, Joseph A

    2015-06-19

    The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back-gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back-gate electrode potential. This sudden variation in phonon intensity is asymmetric in the carrier type, depending on the sign of the tunneling bias. PMID:26196985

  7. 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.

  8. Coulomb Repulsion Effect in Two-electron Non-adiabatic Tunneling through a One-level redox Molecule

    DEFF Research Database (Denmark)

    Medvedev, Igor M.; Kuznetsov, Alexander M.; Ulstrup, Jens

    2009-01-01

    We investigated Coulomb repulsion effects in nonadiabatic (diabatic) two-electron tunneling through a redox molecule with a single electronic level in a symmetric electrochemical contact under ambient conditions, i.e., room temperature and condensed matter environment. The electrochemical contact is representative of electrochemical scanning tunneling microscopy or a pair of electrochemical nanoscale electrodes. The two-electron transfer molecular system also represents redox molecules with thre...

  9. Reviewing the Electronic Resources & Libraries Conference

    Science.gov (United States)

    Tijerina, Bonnie

    2008-01-01

    The third Electronic Resources & Libraries (ER&L) conference gathered at Georgia Institute of Technology's Global Learning and Conference Center in Atlanta, Georgia, March 18-21, 2008. Over 360 attendees, from six countries and from 80% of the United States, represented their libraries and organizations resulting in a diverse and informative…

  10. 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.

  11. Interplay between adsorbate diffusion and electron tunneling at an insulating surface

    International Nuclear Information System (INIS)

    We investigate electron tunneling between defects and mobile adsorbates on the surface of MgO and show that electrons can be transferred to Au and Pt atoms from defects, such as oxygen vacancies, over distances ?20 A even at room temperature. As a result of the surface-mediated interaction following electron transfer, the mobility of these metal atoms is enhanced significantly. Such processes may affect the kinetics of growth and structure of adsorbed clusters and thin films and the interaction of molecules with surfaces.

  12. Sensitivity of tunneling-rotational transitions in ethylene glycol to variation of electron-to-proton mass ratio

    Science.gov (United States)

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

    2014-06-01

    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 ?, this spectrum is highly sensitive to the possible ? variation. We used simple 14 parameter effective Hamiltonian to calculate dimensionless sensitivity coefficients Q? of the tunneling-rotational transitions and found that they lie in the range from -17 to +18. Ethylene glycol has been detected in the interstellar medium. All this makes it one of the most sensitive probes of ? variation at the large space and time scales.

  13. 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.

  14. Ultralarge area MOS tunnel devices for electron emission

    DEFF Research Database (Denmark)

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm; Johansson, Martin; Hansen, Ole; Chorkendorff, Ib

    2007-01-01

    A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxide) MOS capacitors have been fabricated to investigate their functionality and the variations in oxide thickness, with the use as future electron emission devices as the goal. I-V characteristics show ver...

  15. Ultralarge area MOS tunnel devices for electron emission

    OpenAIRE

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm; Johansson, Martin; Hansen, Ole; Chorkendorff, Ib

    2008-01-01

    A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxide) MOS capacitors have been fabricated to investigate their functionality and the variations in oxide thickness, with the use as future electron emission devices as the goal. I-V characteristics show ...

  16. Electron population inversion of dimensional quantization subbands at longitudinal transport in tunnel-coupled quantum wells

    International Nuclear Information System (INIS)

    A laser scheme for generation of far infrared radiation (? ? 150 ?m) is proposed. The population inversion of subbands can be provided by electron transport in a triple tunnel-coupled quantum well under strong electric field. Of importance is the fact that the structure proposed contains a single rough heterointerface. The Monte-Carlo simulation of the electron transport in AlxGa1-xAs/GaAs (x = 0.2, 0.3) triple tunnel-coupled quantum well heterostructure has shown a population inversion of the first and second subbands that appears when the applied field exceeds 1.2 kV/cm at T = 4.2 K and 300 K

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

    OpenAIRE

    Preisinger, M.; Krispin, 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...

  18. 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.

  19. STM Study of Encapsulated Nanometer Size Gold Clusters: Room Temperature Single Electron Tunneling Effects

    Science.gov (United States)

    Hong, S.; Bielefeld, J. D.; Andres, R. P.; Reifenberger, R.

    1997-03-01

    New measurements of I(V,z) from nanometer-size crystalline Au clusters using an UHV STM are reported. In contrast to previous studies,[1,2,3] Au clusters are now encapsulated by dodecanethiol molecules. After encapsulation, the clusters are deposited on either a freshly cleaved MoS2 substrate or on a Au(111) film coated with a self assembled monolayer (SAM) of a double ended thiol, p-xylene-?,?'-dithiol (C_8H_10S2 ). STM images of the encapsulated clusters supported on either substrate reveal a regular, hexagonal closed packed array. I(V,Z) data obtained from isolated clusters exhibit reproducible single electron tunneling behavior. By using the same STM tip, the size dependence of the single electron tunneling features in the I(V,z) data can be studied reliably. By fitting the measured I(V,z) data to the semiclassical theory for Coulomb blockade, the electronic properties of the tunnel junction between cluster and substrate can be determined. \\vspace11pt [1]. M. Dorogi, et al., Phys. Rev. B52, 9071 (1995). [2]. R.P. Andres, et al., Science 272, 1323 (1996). [3]. Samanta, et al., Phys. Rev. B53, 7626 (1996).

  20. Electronic Resources and Web Sites: Replacing a Back-end Database with Innovative's Electronic Resource Management

    OpenAIRE

    Tull, Laura

    2013-01-01

    In the fall of 2002, Ohio State University along with the University of Washington, the University of Western Australia, Washington State University, and Glasgow University entered into a development partnership with Innovative Interfaces. The goal was to develop a module to manage electronic resources, integrated into Innovative’s Millennium library system. The product, Electronic Resource Management (ERM), became available in 2004 and is based on the work of the Digital Library Federation E...

  1. 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...

  2. 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.

  3. 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.

  4. 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.

  5. Detection and Cloaking of Molecular Objects in Coherent Nanostructures Using Inelastic Electron Tunneling Spectroscopy

    CERN Document Server

    Fransson, J; Balatsky, A V; 10.1021/nl903991a

    2010-01-01

    We address quantum invisibility in the context of electronics in nanoscale quantum structures. We make use of the freedom of design that quantum corrals provide and show that quantum mechanical objects can be hidden inside the corral, with respect to inelastic electron scattering spectroscopy in combination with scanning tunneling microscopy, and we propose a design strategy. A simple illustration of the invisibility is given in terms of an elliptic quantum corral containing a molecule, with a local vibrational mode, at one of the foci. Our work has implications to quantum information technology and presents new tools for nonlocal quantum detection and distinguishing between different molecules.

  6. Single-electron tunneling by using a two-dimensional Corbino nano-scale disk

    Directory of Open Access Journals (Sweden)

    H. Taira

    2015-09-01

    Full Text Available We investigate a single-electron tunneling effect of two-dimensional electron systems formed in the Corbino nano-scale disk. By controlling bias and gate voltages, the transistor using this effect is able to control electrons one by one. The present study focuses on the electronic transmission probability affected by the charging energy in the Corbino-type single-electron transistor. We reformulated the Schrödinger equation for an electron in the Corbino disk in order to consider the effect of the curvature of the disk, taking into account the charging effect on the performance of the Corbino-type single-electron transistor. We formulated the transmission probability of the electron by applying the Wentzel-Kramers-Brillouin (WKB method. The electron’s energy in the formula of the transmission probability is then associated to the energy eigenvalue of the Schrödinger equation for an electron in an effective confining potential. We numerically solved the Schrödinger equation to evaluate the transmission probability. Our results show that the transmission probability strongly depends on the charging energy stored in the Corbino disk depending on its size.

  7. Making sense of the electronic resource marketplace: trends in health-related electronic resources.

    Science.gov (United States)

    Blansit, B D; Connor, E

    1999-07-01

    Changes in the practice of medicine and technological developments offer librarians unprecedented opportunities to select and organize electronic resources, use the Web to deliver content throughout the organization, and improve knowledge at the point of need. The confusing array of available products, access routes, and pricing plans makes it difficult to anticipate the needs of users, identify the top resources, budget effectively, make sound collection management decisions, and organize the resources effectively and seamlessly. The electronic resource marketplace requires much vigilance, considerable patience, and continuous evaluation. There are several strategies that librarians can employ to stay ahead of the electronic resource curve, including taking advantage of free trials from publishers; marketing free trials and involving users in evaluating new products; watching and testing products marketed to the clientele; agreeing to beta test new products and services; working with aggregators or republishers; joining vendor advisory boards; benchmarking institutional resources against five to eight competitors; and forming or joining a consortium for group negotiating and purchasing. This article provides a brief snapshot of leading biomedical resources; showcases several libraries that have excelled in identifying, acquiring, and organizing electronic resources; and discusses strategies and trends of potential interest to biomedical librarians, especially those working in hospital settings. PMID:10427421

  8. Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy.

    Science.gov (United States)

    Jung, Suyong; Park, Minkyu; Park, Jaesung; Jeong, Tae-Young; Kim, Ho-Jong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Hwang, Chanyong; Kim, Yong-Sung

    2015-01-01

    Inelastic electron tunneling spectroscopy is a powerful technique for investigating lattice dynamics of nanoscale systems including graphene and small molecules, but establishing a stable tunnel junction is considered as a major hurdle in expanding the scope of tunneling experiments. Hexagonal boron nitride is a pivotal component in two-dimensional Van der Waals heterostructures as a high-quality insulating material due to its large energy gap and chemical-mechanical stability. Here we present planar graphene/h-BN-heterostructure tunneling devices utilizing thin h-BN as a tunneling insulator. With much improved h-BN-tunneling-junction stability, we are able to probe all possible phonon modes of h-BN and graphite/graphene at ? and K high symmetry points by inelastic tunneling spectroscopy. Additionally, we observe that low-frequency out-of-plane vibrations of h-BN and graphene lattices are significantly modified at heterostructure interfaces. Equipped with an external back gate, we can also detect high-order coupling phenomena between phonons and plasmons, demonstrating that h-BN-based tunneling device is a wonderful playground for investigating electron-phonon couplings in low-dimensional systems. PMID:26563740

  9. Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy

    Science.gov (United States)

    Jung, Suyong; Park, Minkyu; Park, Jaesung; Jeong, Tae-Young; Kim, Ho-Jong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Hwang, Chanyong; Kim, Yong-Sung

    2015-11-01

    Inelastic electron tunneling spectroscopy is a powerful technique for investigating lattice dynamics of nanoscale systems including graphene and small molecules, but establishing a stable tunnel junction is considered as a major hurdle in expanding the scope of tunneling experiments. Hexagonal boron nitride is a pivotal component in two-dimensional Van der Waals heterostructures as a high-quality insulating material due to its large energy gap and chemical-mechanical stability. Here we present planar graphene/h-BN-heterostructure tunneling devices utilizing thin h-BN as a tunneling insulator. With much improved h-BN-tunneling-junction stability, we are able to probe all possible phonon modes of h-BN and graphite/graphene at ? and K high symmetry points by inelastic tunneling spectroscopy. Additionally, we observe that low-frequency out-of-plane vibrations of h-BN and graphene lattices are significantly modified at heterostructure interfaces. Equipped with an external back gate, we can also detect high-order coupling phenomena between phonons and plasmons, demonstrating that h-BN-based tunneling device is a wonderful playground for investigating electron-phonon couplings in low-dimensional systems.

  10. 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.

  11. Single-electron tunneling by using a two-dimensional Corbino nano-scale disk

    Science.gov (United States)

    Taira, H.; Suzuki, A.

    2015-09-01

    We investigate a single-electron tunneling effect of two-dimensional electron systems formed in the Corbino nano-scale disk. By controlling bias and gate voltages, the transistor using this effect is able to control electrons one by one. The present study focuses on the electronic transmission probability affected by the charging energy in the Corbino-type single-electron transistor. We reformulated the Schrödinger equation for an electron in the Corbino disk in order to consider the effect of the curvature of the disk, taking into account the charging effect on the performance of the Corbino-type single-electron transistor. We formulated the transmission probability of the electron by applying the Wentzel-Kramers-Brillouin (WKB) method. The electron's energy in the formula of the transmission probability is then associated to the energy eigenvalue of the Schrödinger equation for an electron in an effective confining potential. We numerically solved the Schrödinger equation to evaluate the transmission probability. Our results show that the transmission probability strongly depends on the charging energy stored in the Corbino disk depending on its size.

  12. Bistability of single cyclooctadiene molecules on Si(001) induced by inelastic electron tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Nacci, Christophe; Lagoute, Jerome; Liu, Xi; Foelsch, Stefan [Paul Drude Institute for Solid-State Electronics, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2008-07-01

    The tip-induced switching of single 1,5 cyclooctadiene molecules (COD) on Si(001) was studied by low-temperature scanning tunneling microscopy. COD (C{sub 8}H{sub 12}) is a cyclic alkene with a twisted boat double-degenerate configuration which adsorbs in two different structures: the so-called bridge structure and the upright structure, with the bridge structure being the prevalent conformation. Time spectroscopy of the tunnel current with the tip positioned over the molecule adsorbed in the bridge structure reveals fluctuations between two levels of current reminiscent to statistical telegraph noise. This behavior is interpreted as a reversible dynamic switching of the adsorbed molecule between two degenerate conformations triggered by inelastic single-electron excitation. First measurements on COD adsorbed in the upright structure reveal a significantly different noise response with an enhanced quantum yield and a lifted degeneracy of the current level population probabilities.

  13. Electron radiation effect on excess currents of GaSb tunnel diodes

    International Nuclear Information System (INIS)

    Straight lines of the volt ampere characteristics VAC of GaSb tunnel diodes were investigated. Four sections with different current transfer mechanisms are distinguished in the region of excess currents on the VAC of intact diodes. An increase in the excess current accompanied by a change in the current transfer mechanisms is observed on certain VAC sections following irradiation by 2.2 MeV electrons. The increase in the excess current is related to the formation and rearrangement of radiation defects responsible for shallow and deep levels in the forbidden GaSb zone. The energy levels measured by method of tunnel spectroscopy are found to be: Esub(c)-0.060 and Esub(c)-0.2 eV in the n-region of the p-n-transition

  14. 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...

  15. A density-functional theory study of tip electronic structures in scanning tunneling microscopy

    International Nuclear Information System (INIS)

    In this work, we report a detailed analysis of the atomic and electronic structures of transition metal scanning tunneling microscopy tips: Rh, Pd, W, Ir, and Pt pyramidal models, and transition metal (TM) atom tips supported on the W surface, by means of ab initio density-functional theory methods. The d electrons of the apex atoms of the TM tips (Rh, Pd, W, Ir, and Pt tetrahedral structures) show different behaviors near the Fermi level and, especially for the W tip, dz2 states are shown to be predominant near the Fermi level. The electronic structures of larger pyramidal TM tip structures with a single apex atom are also reported. Their obtained density of states are thoroughly discussed in terms of the different d-electron occupations of the TM tips. (paper)

  16. Atomic-scale mapping of electronic structures across heterointerfaces by cross-sectional scanning tunneling microscopy

    Science.gov (United States)

    Chiu, Ya-Ping; Huang, Bo-Chao; Shih, Min-Chuan; Huang, Po-Cheng; Chen, Chun-Wei

    2015-09-01

    Interfacial science has received much attention recently based on the development of state-of-the-art analytical tools that can create and manipulate the charge, spin, orbital, and lattice degrees of freedom at interfaces. Motivated by the importance of nanoscale interfacial science that governs device operation, we present a technique to probe the electronic characteristics of heterointerfaces with atomic resolution. In this work, the interfacial characteristics of heteroepitaxial structures are investigated and the fundamental mechanisms that pertain in these systems are elucidated through cross-sectional scanning tunneling microscopy (XSTM). The XSTM technique is employed here to directly observe epitaxial interfacial structures and probe local electronic properties with atomic-level capability. Scanning tunneling microscopy and spectroscopy experiments with atomic precision provide insight into the origin and spatial distribution of electronic properties across heterointerfaces. The first part of this report provides a brief description of the cleavage technique and spectroscopy analysis in XSTM measurements. The second part addresses interfacial electronic structures of several model heterostructures in current condensed matter research using XSTM. Topics to be discussed include high-?‘s/III-V’s semiconductors, polymer heterojunctions, and complex oxide heterostructures, which are all material systems whose investigation using this technique is expected to benefit the research community. Finally, practical aspects and perspectives of using XSTM in interface science are presented.

  17. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS Initiatives

    Directory of Open Access Journals (Sweden)

    John Paul Anbu K.

    2013-07-01

    Full Text Available Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the specific resource from the gamut of other resources followed by acquisition of the specific resource into the library realm and then felicitating access to the users and then the follow-up of studying the usage of the resource for further continuation of those resources. In between these processes there is the cumbersome chore of going through the licensing agreements and keeping the records correct. All these processes are time consuming and involve a lot of work. These relentless arrays of work have made librarians to look for systems which can save their time and energy and provide efficient management of e-resources. This paper looks at the origin of the ERMS (E-resource Management Systems and the available ERMS in the library digital landscape.

  18. 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.

  19. 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

  20. 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.

  1. Making sense of the electronic resource marketplace: trends in health-related electronic resources.

    OpenAIRE

    Blansit, B D; Connor, E

    1999-01-01

    Changes in the practice of medicine and technological developments offer librarians unprecedented opportunities to select and organize electronic resources, use the Web to deliver content throughout the organization, and improve knowledge at the point of need. The confusing array of available products, access routes, and pricing plans makes it difficult to anticipate the needs of users, identify the top resources, budget effectively, make sound collection management decisions, and organize th...

  2. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    International Nuclear Information System (INIS)

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al2O3/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al2O3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al2O3 valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance

  3. Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wei [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V., E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Bijesh, R.; Datta, S. [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei, E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China)

    2014-11-24

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al{sub 2}O{sub 3}/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al{sub 2}O{sub 3} conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al{sub 2}O{sub 3} valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance.

  4. Electronic properties of (Zn,CoO systems probed by scanning tunnelling spectroscopy

    Directory of Open Access Journals (Sweden)

    L. Moldovan

    2008-05-01

    Full Text Available The aim of this paper is to gain insight into theelectronic properties of (Zn,CoO system - a widebandgap Diluted Magnetic Semiconductors (DMSshowing room temperature (RT ferromagnetism undern-type doping conditions. On the experimental side, ultrahigh-vacuum scanning tunnelling microscopy andspectroscopy (STM and STS at variable temperature (Tare used to probe the local electronic structure of thesystem. It is presented the map of the local density ofstates (LDOS of polar ZnO surfaces. Then, it is possibleto decorate (incorporate Co atoms onto (into thesemiconductor.

  5. 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

  6. 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

  7. From Tedious to Timely: Screencasting to Troubleshoot Electronic Resource Issues

    Science.gov (United States)

    Hartnett, Eric; Thompson, Carole

    2010-01-01

    The shift from traditional print materials to electronic resources, in conjunction with the rise in the number of distance education programs, has left many electronic resource librarians scrambling to keep up with the resulting inundation of electronic resource problems. When it comes to diagnosing these problems, words do not always convey all…

  8. Electron radiation effect on volt-farad characteristics of MDC-structures with tunnel-thin dielectric

    International Nuclear Information System (INIS)

    Effect of electron radiation in the 5-20 keV energy and 3.10-3-3.10-1 Cal/cm2 dose ranges on voltfarad characteristics of MOS structures with tunnel-thin dielectric is investigated. Electron radiation is shown to reproducibly vary the value of built- in charge and density of surface states

  9. Tunneling Hamiltonian

    OpenAIRE

    Kern, Johannes

    2013-01-01

    For the description of the transport of electrons across a quantum dot, which is tunnel coupled to leads at different chemical potentials, it is usual to assume that the total Hamiltonian of the composite system of the leads and the quantum dot is the sum of three contributions: That of the leads (noninteracting electrons), that of the quantum dot and a third one, the "tunneling Hamiltonian", which reflects the possibility that electrons can move from the leads to the quantu...

  10. 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.

  11. Opto-electronic studies of semiconductor tunnelling structures and quantum wells

    International Nuclear Information System (INIS)

    This thesis describes optical and electrical studies of two groups of low dimensional semiconductor structures. The majority of the work concerns an optical study of electron populations (n1,n2) in the ground (E1) and first excited (E2) states of the quantum well (QW) regions of various GaAs-AlGaAs double and triple barrier resonant tunnelling structures (DBRTS and TBRTS respectively). The relative populations of the E2 and E1 confined states are determined from analysis of the photoluminescence (PL) intensities. When the structures are biased for tunnelling into the E2 state, rate equation analysis shows that n2/n1 is approximately equal to ?i/?1, where ?i is the E2-E1 intersubband scattering time and ?1 is the tunnelling-out time from E1. The relative electron populations are thus expected to be a sensitive function of the QW and collector barrier widths. The second group of structures studied in this thesis consists of a series of shallow GaAs-AlyGa1-yAs multi-quantum well structures, with aluminium concentrations of 1 to 4.5%. The 1s-2s exciton energy separation is measured from PL excitation (PLE) experiments and is combined with a small correction for the 2s binding energy to give an accurate determination of the exciton binding energy (Ex). It is found that even in these very shallow QW structures there is a marked enhancement in the value of Ex over that in 3D GaAs

  12. 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...

  13. Equilibrium and space-charge wave analysis of electron beams in conducting and absorbing gyrotron beam tunnels

    International Nuclear Information System (INIS)

    The fluid equations for an electron beam are used to calculate the equilibrium velocity and density profiles, limiting current and space-charge wave properties of an annular beam undergoing magnetic compression in a gyrotron beam tunnel. Both non-relativistic and relativistic equations are derived. The beam tunnel may have a conventional smooth wall or an absorbing dielectric-loaded wall. Small values of magnetic compression are seen to have a large effect on the profiles and the current limit of a given tunnel. Common dielectric-loaded tunnels are also seen to reduce the limiting current by 5-20%. Limiting current data for a wide range of beam parameters are shown. The dispersion relation for a convective instability arising from the gradient in the equilibrium potential depression profiles is derived using the linearized fluid equations. The growth rate is seen to increase for increasing current and pitch angle, and for increasing wall effects of an absorbing tunnel. The average growth rate is calculated for a typical gyrotron beam and beam tunnel as well as for a beam entering an interaction cavity. Growth rates for all values of kz are seen to decrese for a conventional conducting beam tunnel in a constant magnetic field. (author) 13 figs., refs

  14. Time-dependent tunneling of spin-polarized electrons in coupled quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Cruz, H; Luis, D [Departamento de Fisica Basica, Universidad de La Laguna, 38204 La Laguna, Tenerife (Spain)], E-mail: hcruz@ull.es

    2008-02-15

    We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations.

  15. Magnetooscillations of the tunneling current between two-dimensional electron systems

    International Nuclear Information System (INIS)

    We calculate electric current caused by electron tunnelling between two-dimensional layers in the magnetic field applied perpendicular to the layers. An elastic scattering of the electrons is taken into account. Analytical results are obtained for two regimes: i) small magnetic field, when the Landau quantization is suppressed by the scattering and the oscillatory part of the current shows nearly harmonic behaviour; ii) high magnetic field, when the Landau levels are well-defined and the conductivity shows series of sharp peaks corresponding to resonant magnetotunneling. In the last case, we used two alternative approaches: self-consistent Born approximation and path integral method, and compared obtained results. (author). 12 refs, 3 figs

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

    CERN Document Server

    Viatkina, A V

    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-rotational transitions and found that they lie in the range from $-17$ to $+18$. Ethylene glycol has been detected in the interstellar medium. All this makes it one of the most sensitive probes of $\\mu$ variation at the large space and time scales.

  17. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared with the molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new approach to imaging of biological processes directly in aqueous medium. We provide first an extension of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between the substrate and tip Fermi levels. STM here involves coherent two-step interfacial electron transfer between the redox level and the enclosing substrate and tip. We have also extended previous experimental in situ STM studies of the blue copper protein Pseudomonas aeruginosa azurin, adsorbed on Au(111), to cover a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent adsorbate coverage decrease outside this range. This could reflect in part redox processes of azurin, but also tip-induced disassembly of the azurin monolayer.

  18. An atomic switch of electron propagation on Ge (001) by tunneling carrier injection

    Science.gov (United States)

    Komori, Fumio

    2008-03-01

    Reversible switching of electronic conduction through atom manipulation is one of the important subjects of nanoscience. However, different conducting pathways were not clearly observed with atomic resolution. We have demonstrated the correlation between the change of surface atomic position by tunneling carrier injection and that of the reflection of one-dimensional (1D) surface-state electrons on the Ge (001) surface with a low density of heterogeneous Sn-Ge dimers. [1] On the clean Ge(001) surface, two adjacent atoms form a buckled dimer, and the buckling orientation of the Ge dimer can be locally and reversibly controlled by carrier injection to the surface from the STM tip. [2] The unoccupied surface &*circ;-electron behaves like a 1D free electron along the Ge dimer row. When Sn atoms are deposited on the clean Ge(001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge dimer position in the surface. [3] An atomic switch is realized for the &*circ; electrons in the Ge dimer- row direction by injection carriers to reversibly flip the buckling orientation of a single Sn-Ge dimer in the dimer row. When the Sn atom of the heterogeneous dimer is at the lower position, the 1D electrons are reflected and a standing wave of this state is observed. Whereas, when it is at the upper position, the 1D electrons pass through the heterogeneous dimer, and no standing wave is observed. In this state, the lower atom of the dimer is Ge, and the &*circ; state at the dimer is little different from that of the Ge-Ge dimers. [1] K. Tomatsu, K. Nakatsuji, T. Iimori, Y. Takagi, H. Kusuhara, A. Ishii, F. Komori; Science 315, 1696, 2007. [2] Y. Takagi, Y. Yoshimoto, K. Nakatsuji, F. Komori; Surf. Sci. 559, 1, 2004. [3] K. Tomatsu, K. Nakatsuji, T. Iimori, F. Komori; Surf. Sci. 601, 1736, 2007.

  19. Comment on ‘Germanium electron–hole bilayer tunnel field-effect transistors with a symmetrically arranged double gate’

    Science.gov (United States)

    Padilla, J. L.; Alper, C.; Gámiz, F.; Ionescu, A. M.

    2015-12-01

    In this comment we demonstrate that the inclusion of field-induced quantum confinement effects through appropriate discretization of conduction and valence bands refutes the suitability of a germanium electron–hole bilayer tunnel field-effect transistor with symmetrically arranged gates (Jeong et al 2015 Semicond. Sci. Technol. 30 035021). Delayed alignment of the first electron and hole energy subbands in the central gated intrinsic channel region makes the onset of vertical band-to-band tunneling unattainable at low applied voltages for the metal workfunctions used by Jeong et al. Furthermore, quantization effects lead to the appearance of unavoidable parasitic lateral tunneling to the lightly doped drain-source region (LDD), which seriously degrades the switching behavior reported by Jeong et al.

  20. Chemical imaging of latent fingerprints by mass spectrometry based on laser activated electron tunneling.

    Science.gov (United States)

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

    2015-03-01

    Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints. PMID:25647159

  1. User Perception of Electronic Resources in the University of Ilorin

    OpenAIRE

    BASHORUN; M. Tunji; ISAH Abdulmumin; M.Y ADISA

    2011-01-01

    This study examined the user perception of the electronic resources by the academic staff of the University of Ilorin. The sample consists of 250 academic staff selected from eight (8) out of the twelve (12) faculties that made up of the university. Data were collected through an electronic resources user perceptional survey (ERUPS). Responses were received from 225 (90%) academic staff of the eight faculties. Analysis revealed frequency of use of electronic resources was low. Reasons allu...

  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. 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.

  4. Detailed analysis of water structure in a solvent mediated electron tunneling mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Negre, Christian F A; Sanchez, Cristian G [Departamento de Matematica y Fisica, Facultad de Ciencias Quimicas, INFIQC, Universidad Nacional de Cordoba, Ciudad Universitaria, Cordoba (Argentina); Jara, Gabriel E; Pierini, Adriana B [Departamento de Quimica Organica, Facultad de Ciencias Quimicas, INFIQC, Universidad Nacional de Cordoba, Ciudad Universitaria, Cordoba (Argentina); Vera, D Mariano A, E-mail: cgsanchez@fcq.unc.edu.ar [Departamento de Quimica, Facultad de Ciencias Exactas, Universidad Nacional de Mar del Plata, Mar del Plata (Argentina)

    2011-06-22

    This work aims at describing the water structure characteristics that influence the electron transfer superexchange mechanism by explicitly calculating the solvent mediated conductance between the donor and acceptor in a generic pair. The method employed here is based on the non-equilibrium Green function formalism for calculating the conductance over solvent trajectories previously determined by molecular dynamics methods. A non-exponential dependence of the conductance is observed with respect to the distance between the donor and the acceptor. Local fluctuations of the solvent structure are responsible for the non-monotonic dependence, mainly due to the formation of solvent bridges that act as a molecular wire connecting the sites. This shortcutting phenomenon is observed for certain ranges of distances between the donor and acceptor in the pair. Charge on the sites strongly affects the local solvent structure and causes qualitative changes in the distance dependence of the tunneling probability.

  5. 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.

  6. 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.

  7. 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 ...

  8. Electron-tunneling modulation in percolating network of graphene quantum dots: fabrication, phenomenological understanding, and humidity/pressure sensing applications.

    Science.gov (United States)

    Sreeprasad, T S; Rodriguez, Alfredo Alexander; Colston, Jonathan; Graham, Augustus; Shishkin, Evgeniy; Pallem, Vasanta; Berry, Vikas

    2013-04-10

    The two-dimensional (2D) electron cloud, flexible carbon-carbon bonds, chemical modifiability, and size-dependent quantum-confinement and capacitance makes graphene nanostructures (GN) a widely tunable material for electronics. Here we report the oxidation-led edge-roughening and cleavage of long graphene nanoribbons (GNRs) (150 nm wide) synthesized via nanotomy (nanoscale cutting) of graphite (with 2 nm edged diamond knife) to produce graphene quantum dots (GQD). These GQDs (~100-200 nm) selectively interfaced with polyelectrolyte microfiber (diameter = 2-20 ?m) form an electrically percolating-network exhibiting a characteristic Coulomb blockade signature with a dry tunneling distance of 0.58 nm and conduction activation energy of 3 meV. We implement this construct to demonstrate the functioning of humidity and pressure sensors and outline their governing model. Here, a 0.36 nm decrease in the average tunneling-barrier-width between GQDs (tunneling barrier = 5.11 eV) increases the conductivity of the device by 43-fold. These devices leverage the modulation in electron tunneling distances caused by pressure and humidity induced water transport across the hygroscopic polymer microfiber (Henry's constant = 0.215 Torr(-1)). This is the foremost example of GQD-based electronic sensors. We envision that this polymer-interfaced GQD percolating network will evolve a new class of sensors leveraging the low mass, low capacitance, high conductivity, and high sensitivity of GQD and the interfacial or dielectric properties of the polymer fiber. PMID:23506081

  9. Chiral Enhanced Phonon Excitations in Inelastic Electron Tunneling Spectroscopy of Graphene

    Science.gov (United States)

    Natterer, Fabian Donat

    2015-03-01

    In graphene, phonons are important agents for a wide range of phenomena; they mediate relaxation rates for hot carriers, they lead to van-Hove singularities, and they induce a renormalization of the Fermi velocity due to electron-phonon coupling and many-body interactions. The previous observations of phonons by inelastic electron tunneling spectroscopy (IETS) have been expandable in terms of detail and resolution, due to weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. We find that utilizing a back gated graphene device, where the graphene charge carrier density can be varied in magnitude and sign, allows all the critical point graphene phonons with large density of states to be sampled by IETS with the scanning tunneling microscope, and in good agreement with density functional calculations. In addition, a strong overtone excitation at 360 meV is observed. Quite surprisingly, we observe all the graphene excitations are resonantly enhanced when the charge carrier type is switched, indicating that this amplification occurs whenever the inelastic transition allows a change in the graphene chirality. The chiral enhancement is observed to follow a linear trend with energy and reaches almost an order of magnitude for the highest transition. Our averaging technique suppresses charge carrier dependent excitations, while it improves the signal for inelastic transitions. This approach can be employed as a guide in advanced studies that are relying on gate tunable graphene devices, such as for the detection of spin, vibrational, or rotational excitations in adsorbates. Collaborators: Y. Zhao* , J. Wyrick* , W. Y. Ruan** , Y-H. Chan** , M-Y. Chou** , N. B. Zhitenev* , J. A. Stroscio* : * NIST/CNST, ** Georgia Tech, FDN appreciates funding from the SNF foundation under Project No. 148891.

  10. 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.

  11. Use of Electronic Resources in Scholarly Electronic Journals: A Citation Analysis.

    Science.gov (United States)

    Herring, Susan Davis

    2002-01-01

    Describes a citation analysis of research articles from scholarly electronic journals published in 1999-2000 that focused on the extent to which scholars are using electronic resources and the types and subject areas of online resources that are being referenced. Results indicate a growing reliance on electronic resources, especially…

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

    OpenAIRE

    Voitsekhivska, O. M.; Ju.O.Seti; M.V.Tkach

    2012-01-01

    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...

  13. 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…

  14. What Faculty Think: A Survey on Electronic Resources

    Science.gov (United States)

    Jackson, Millie

    2008-01-01

    In the fall of 2007, ebrary surveyed 906 faculty from around the world, asking them how they used electronic resources. This article, focusing on the responses of faculty to a few survey questions, finds some expected and surprising attitudes that faculty have about electronic resources for their own and students' research. (Contains 2 notes.)

  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. 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.

  17. 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.

  18. 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.)

  19. Laser Activated Electron Tunneling Based Mass Spectrometric Imaging of Molecular Architectures of Mouse Brain Revealing Regional Specific Lipids.

    Science.gov (United States)

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

    2016-01-01

    A comprehensive description of overall brain architecture at the molecular level is essential for understanding behavioral and cognitive processes in health and diseases. Although fluorescent labeling of target proteins has been successfully established to visualize a brain connectome, the molecular basis for diverse neurophysiological phenomena remains largely unknown. Here we report a brain-wide, molecular-level, and microscale imaging of endogenous metabolites, in particular, lipids of mouse brain by using laser activated electron tunneling (LAET) and mass spectrometry. In this approach, atomic electron emission along with finely tuned laser beam size provides high resolution that can be down to the sub-micrometer level to display spatial distribution of lipids in mouse brain slices. Electron-directed soft ionization has been achieved through exothermal capture of tunneling photoelectrons as well as unpaired electron-initiated chemical bond cleavages. Regionally specific lipids including saturated, mono-unsaturated, and poly-unsaturated fatty acids as well as other lipids, which may be implicated in neurological signaling pathways, have been discovered by using this laser activated electron tunneling based mass spectrometric imaging (LAET-MSI) technique. PMID:26613184

  20. 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.

  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. You Have "How Many" Spreadsheets? Rethinking Electronic Resource Management

    Science.gov (United States)

    Rux, Erika; Borchert, Theresa

    2010-01-01

    As libraries face a veritable explosion of electronic resources and as the interconnectedness of print and online resources becomes increasingly complicated, many librarians are challenged to find efficient and cost-friendly ways to manage these resources. In this article, the authors describe how a team of people from various library departments…

  3. Coulomb Repulsion Effect in Two-electron Non-adiabatic Tunneling through a One-level redox Molecule

    DEFF Research Database (Denmark)

    Medvedev, Igor M.; Kuznetsov, Alexander M.

    2009-01-01

    We investigated Coulomb repulsion effects in nonadiabatic (diabatic) two-electron tunneling through a redox molecule with a single electronic level in a symmetric electrochemical contact under ambient conditions, i.e., room temperature and condensed matter environment. The electrochemical contact is representative of electrochemical scanning tunneling microscopy or a pair of electrochemical nanoscale electrodes. The two-electron transfer molecular system also represents redox molecules with three electrochemically accessible oxidation states, rather than only two states such as comprehensively studied. It is shown that depending on the effective Coulomb repulsion energy, the current/overpotential relation at fixed bias voltage shows two narrow (~kBT) peaks in the limit of strong electron-phonon coupling to the solvent environment. The system also displays current/bias voltage rectification. The differential conductance/bias voltage correlation can have up to four peaks even for a single-level redox molecule. The peak position, height, and width are determined by the oxidized and reduced states of both the ionization and affinity levels of the molecule and depend crucially on the Debye screening of the electric field in the tunneling gap. ©2009 American Institute of Physics

  4. 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.

  5. 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…

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

    International Nuclear Information System (INIS)

    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

  7. ?- X electron transfer in type II tunneling bi-quantum wells

    Science.gov (United States)

    Tackeuchi, Atsushi; Strauß, Uwe; Rühle, Wolfgang W.; Inata, Tsuguo; Muto, Shunichi

    1994-06-01

    We have studied the energy band structure and the ?- X carrier transfer mechanism for type II tunneling bi-quantum wells consisting of GaAs wells, AlGaAs barriers of different thicknesses, and AlAs layers by cw and time-resolved photoluminescence measurements. The cw photoluminescence spectra of the indirect recombination of X electrons in the 7.1 nm thick AlAs layers with ? holes in the 2.8 nm thick GaAs wells show weak zero-phonon lines indicating that the AlAs confined states at Xxy are lower than those at Yz. Time-resolved photoluminescence reveals that the carrier transfer time depends stronger on temperature for thicker AlGaAs barriers. Two scattering mechanisms, temperature-dependent phonon scattering and the temperature-independent interface scattering, are probably involved in the carrier transfer, the latter becoming smaller with increasing AlGaAs barrier thickness. Our results are compared with those obtained for similar type II GaAs/AlAs superlattices.

  8. Resonant Tunneling and Persistent Current of a Non-interacting and Weakly Interacting One-dimensional Electron Gas

    OpenAIRE

    Krive, I. V.; Sandström, P.

    1997-01-01

    The persistent current for a one-dimensional ring with two tunnel barriers is considered in the limit of weakly interacting electrons. In addition to a small off-resonance current, there are two kinds of resonant behavior; (i) a current independent of the barrier transparency (true resonance) and (ii) a current analogous to the one for a ring with only a single barrier (``semi''-resonance). For a given barrier transparency one or the other type of resonant behavior is realiz...

  9. Role of the thermoactivated and tunnel electron relaxations of radiation defects in initiation of isothermal exoemission current

    International Nuclear Information System (INIS)

    In this paper aimed at the determination of the role of thermoactivated and tunnel electron-hole recombinations of radiation defects in the appearance of the isothermal exoelectron emission (EEE) current, we carry out the calculation of a value of the isothermal EEE current and make its comparison with the experimental curves of the EEE decay, at various ses of the ultraviolet irradiation of the CsBr alkaline-halide crystals

  10. 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.

  11. Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Zhong Hongying, E-mail: hyzhong@mail.ccnu.edu.cn [Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079 (China); Fu Jieying; Wang Xiaoli; Zheng Shi [Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079 (China)

    2012-06-04

    Highlights: Black-Right-Pointing-Pointer Irradiation of photons with energies more than the band gap generates electron-hole pairs. Black-Right-Pointing-Pointer Electron tunneling probability is dependent on the electron mobility. Black-Right-Pointing-Pointer Tunneling electrons are captured by charge deficient atoms. Black-Right-Pointing-Pointer Unpaired electrons induce cleavages of chemical bonds. - Abstract: Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser ({lambda} = 355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO{sub 2} nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.

  12. Using Zapier with Trello for Electronic Resources Troubleshooting Workflow

    OpenAIRE

    Meghan Finch

    2014-01-01

    Troubleshooting access problems is an important part of the electronic resources management workflow. This article discusses an opportunity to streamline and track troubleshooting using two web-based services: Trello and Zapier.

  13. Some observations on tunnelling of trapped electrons in feldspars and their implications for optical dating

    Science.gov (United States)

    Huntley, D. J.; Lian, Olav B.

    2006-10-01

    Anomalous fading in feldspars is now understood to be caused by the tunnelling of electrons from one defect site to another. Here we present some experimental observations concerning the phenomenon. The fading rates of a variety of feldspar crystals and K-feldspar separates from sediments are reported. It is found that (1) the fading rates of 77 K-feldspar extracts from sediments range from 1 to 10%/decade, with an average value of about 5%/decade, (2) the fading rates of K-feldspars extracted from sediments derived largely from volcanic bedrock are not higher than those from non-volcanic bedrock as is widely thought, (3) the fading rates of 31 individual feldspars range from 1 to 35%/decade, (4) in plagioclase feldspars the fading rate increases with increasing Ca and/or Fe content, (5) the fading rate increases with laboratory radiation dose at large doses, (6) for samples for which the time elapsed since burial is long enough for their luminescence to be in saturation, the fading rate is correlated with the ratio of the field saturation intensity to the laboratory saturation intensity; extrapolation to zero fading rate shows that trap emptying as a result of thermal eviction is not significant, and that the mean thermal lifetime in temperate environments of electrons in traps relevant to dating is ?4 Ma., and (7), different aliquots of a sample can have fading rates that differ by a factor as large as two even if the aliquots contain several thousands of grains, thus it is necessary to ensure when correcting ages for anomalous fading that the fading rate used is that applicable to the aliquots on which the equivalent dose is measured.

  14. Recognition tunneling

    International Nuclear Information System (INIS)

    Single molecules in a tunnel junction can now be interrogated reliably using chemically functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode ('tethered molecule-pair' configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel gap at large currents, and this results in a multiplicity of contacts with a corresponding spread in the measured currents. At small currents (i.e. large gaps) the gap is stable, and functionalizing a pair of electrodes with recognition reagents (the 'free-analyte' configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules. (topical review)

  15. Freshmen's use of library electronic resources and self-efficacy

    OpenAIRE

    Micaela Waldman

    2003-01-01

    To encourage students use of the library, and in particular of its electronic resources, we need to understand what factors encourage students to seek out information in the library setting. Research has shown that self-efficacy influences academic achievement. This paper looks at the role self-efficacy plays in their search for information and use of the library's electronic resources, by surveying a class of freshmen at Baruch College. Their library and computer use were analyzed and correl...

  16. 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.

  17. Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Galbiati, Marta; Tatay, Sergio; Delprat, Sophie; Khanh, Hung Le; Deranlot, Cyrile; Collin, Sophie; Seneor, Pierre, E-mail: pierre.seneor@thalesgroup.com; Mattana, Richard, E-mail: richard.mattana@thalesgroup.com; Petroff, Frédéric [Unité Mixte de Physique CNRS/Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay (France); Servet, Bernard [Thales Research and Technology, 1 Av. A. Fresnel, 91767 Palaiseau (France)

    2015-02-23

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al{sub 2}O{sub 3} or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al{sub 2}O{sub 3}/Alq{sub 3}/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.

  18. Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

    International Nuclear Information System (INIS)

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al2O3 or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al2O3/Alq3/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer

  19. 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

  20. Integrating Electronic Resources into the Library Catalog: A Collaborative Approach.

    Science.gov (United States)

    Herrera, Gail; Aldana, Lynda

    2001-01-01

    Describes a project at the University of Mississippi Libraries to catalog purchased electronic resources so that access to these resources is available only via the Web-based library catalog. Discusses collaboration between cataloging and systems personnel; and describes the MARC catalog record field that contains the information needed to locate…

  1. Using XML Technologies to Organize Electronic Reference Resources

    OpenAIRE

    Huser, Vojtech; Del Fiol, Guilherme; Rocha, Roberto A.

    2005-01-01

    Provision of access to reference electronic resources to clinicians is becoming increasingly important. We have created a framework for librarians to manage access to these resources at an enterprise level, rather than at the individual hospital libraries. We describe initial project requirements, implementation details, and some preliminary results.

  2. Access to electronic resources by visually impaired people

    OpenAIRE

    Jenny Craven

    2003-01-01

    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.

  3. Euler European Libraries and Electronic Resources in Mathematical Sciences

    CERN Document Server

    The Euler Project. Karlsruhe

    The European Libraries and Electronic Resources (EULER) Project in Mathematical Sciences provides the EulerService site for searching out "mathematical resources such as books, pre-prints, web-pages, abstracts, proceedings, serials, technical reports preprints) and NetLab (for Internet resources), this outstanding engine is capable of simple, full, and refined searches. It also offers a browse option, which responds to entries in the author, keyword, and title fields. Further information about the Project is provided at the EULER homepage.

  4. 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. ...

  5. 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.

  6. 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.)

  7. Recognition tunneling.

    Czech Academy of Sciences Publication Activity Database

    Lindsay, S.; He, J.; Sankey, O.; Hapala, Prokop; Jelínek, Pavel; Zhang, P.; Chang, S.; Huang, S.

    2010-01-01

    Ro?. 21, ?. 26 (2010), 262001/1-262001/12. ISSN 0957-4484 R&D Projects: GA ?R GA202/09/0545 Institutional research plan: CEZ:AV0Z10100521 Keywords : STM * tunneling current * molecular electronics * DFT calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.644, year: 2010

  8. 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.

  9. 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 surveys of...

  10. 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.

  11. 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.

  12. 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.

  13. Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor

    Energy Technology Data Exchange (ETDEWEB)

    Moro-Melgar, Diego, E-mail: diego.moro-melgar@obspm.fr [Observatoire de Paris, LERMA, 77 avenue Denfert Rochereau 75014 Paris (France); Mateos, Javier, E-mail: javierm@usal.es; González, Tomás, E-mail: tomasg@usal.es; Vasallo, Beatriz G., E-mail: bgvasallo@usal.es [Departamento de Física Aplicada, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain)

    2014-12-21

    By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current I{sub D} due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current.

  14. Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor

    International Nuclear Information System (INIS)

    By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current ID due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current

  15. Multi-band tight-binding calculation of electronic transport in Fe/trans-polyacetylene/Fe tunnel junctions

    Science.gov (United States)

    Abedi Ravan, B.

    2012-10-01

    In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(px,py,pz) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

  16. 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.

  17. Tunneling between quantum wells

    International Nuclear Information System (INIS)

    Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structures is studied by time-resolved photoluminescence measurements in the pico and femtosecond regime. A large variety of electron and hole resonances is detected when electric fields of both signs are externally applied. The ground state resonance shifts, when the electrons tunnel in the reverse direction, revealing the importance of excitonic effects. Longitudinal optical phonon assisted tunneling plays a minor role for narrow quantum wells in comparison to impurity or interface roughness assisted transfer. Resonant electron tunneling times depend exponentially on the square root of integrated tunneling barrier height and are an order of magnitude faster than resonant hole tunneling times. The n = 2 to n = 1 electronic intersubband scattering time in a 10 nm quantum well is determined to be 550 fs measuring the transfer time through a thin barrier

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

    Energy Technology Data Exchange (ETDEWEB)

    SCHNEIDER,LARRY X.

    2000-06-01

    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.

  19. 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

  20. 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.

  1. 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.

  2. Direct measurement of the maximum tunnel rate in a radio frequency single electron transistor operated as a microwave mixer

    OpenAIRE

    Reilly, D. J.; Buehler, T. M.

    2004-01-01

    By operating the radio frequency single electron transistor (rf-SET) as a mixer we present measurements in which the RC roll-off of the tunnel junctions is observed at high frequencies. Our technique makes use of the non-linear rf-SET transconductance to mix high frequency gate signals and produce difference-frequency components that fall within the bandwidth of the rf-SET. At gate frequencies >15GHz the induced charge on the rf-SET island is altered on time-scales faster th...

  3. Electron transport across capped Au nanoclusters adsorbed in different configurations on highly oriented pyrolytic graphite substrate using scanning tunneling microscopy / spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007 (India)

    2007-04-15

    Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

  4. 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...

  5. 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)

  6. 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…

  7. 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…

  8. 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,…

  9. Electronic Resources: Access and Usage at Ashesi University College

    Science.gov (United States)

    Dadzie, Perpetua S.

    2005-01-01

    Purpose: Sets out to investigate the use of electronic resources by students and faculty of Ashesi University, Ghana, in order to determine the level of use, the type of information accessed and the effectiveness of the library's communication tools for information research. Design/methodology/approach: A questionnaire-based survey was utilized.…

  10. Student Satisfaction with Electronic Library Resources at Wayne State University

    Science.gov (United States)

    Holley, Robert P.; Powell, Ronald R.

    2004-01-01

    This paper reports the results of a survey of student satisfaction with electronic library resources other than the online catalog at Wayne State University. Undertaken in Fall Term 2000 as a class project for a marketing course, a student team designed, administered, and analyzed a survey of a random sample of students. Almost 40% of the…

  11. Discipline, availability of electronic resources and the use of Finnish National Electronic Library - FinELib

    OpenAIRE

    Sanna Torma; Pertti Vakkari

    2004-01-01

    This study elaborated relations between digital library use by university faculty, users' discipline and the availability of key resources in the Finnish National Electronic Library (FinELib), Finnish national digital library, by using nationwide representative survey data. The results show that the perceived availability of key electronic resources by researchers in FinELib was a stronger predictor of the frequency and purpose of use of its services than users' discipline. Regardless of disc...

  12. Discipline, Availability of Electronic Resources and the Use of Finnish National Electronic Library-- FinELib

    Science.gov (United States)

    Törmä, Sanna; Vakkari, Pertti

    2004-01-01

    This study elaborated relations between digital library use by university faculty, users' discipline and the availability of key resources in the Finnish National Electronic Library (FinELib), Finnish national digital library, by using nationwide representative survey data. The results show that the perceived availability of key electronic

  13. Design of a novel on-chip electronic refrigerator based on a normal-insulator-superconductor tunnel junction

    International Nuclear Information System (INIS)

    We present a design for a novel electronic refrigerator having a base temperature of about 18 mK when operating from a bath temperature as high as 1.5 K. This all-electronic refrigerator is a factor of 104 smaller and lighter than dilution and adiabatic demagnetization refrigerators, and is compatible with conventional photolithographic fabrication. The refrigerator, based on the unique thermal transport properties of a normal-insulator-superconductor (NIS) tunnel function, preferentially removes electrons whose energy is higher than the Fermi energy from a normal metal. Electrons with an average energy equal to the Fermi energy are returned to the metal by a superconductor contact. Consequently, high energy thermal excitations are removed from the normal metal, thus cooling the electrons. In our configuration, the junction is deposited on a Si3N4 membrane of submicron thickness that thermally isolates the normal electrode from the bath. As a result, both electrons and phonons in the metal are cooled below the bath temperature. We calculate a cooling power of 2 nW at 100 mK, and a base temperature of 18 mK for a refrigerator area of about 100X100?m2. Using 105 such refrigerator circuits, the cooling power can be increased to 200 ?W

  14. 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.

  15. 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.

  16. 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.

  17. Electronic picture of spin-polarized tunneling with a Cr tip

    Energy Technology Data Exchange (ETDEWEB)

    Czerner, Michael, E-mail: michael.czerner@physik.uni-halle.d [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Rodary, Guillemin; Wedekind, Sebastian [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Fedorov, Dmitry V. [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Sander, Dirk [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Mertig, Ingrid [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany)

    2010-05-15

    We use spin-resolved scanning tunneling spectroscopy with a Cr-covered W-tip to investigate the magnetic switching of single Co islands on Cu(111) in polar magnetic fields. The observed hysteretic curve resembles a shape which is well known from so-called butterfly curves of tunneling magnetoresistance measurements. This indicates that not only the Co-island but also the Cr-tip changes its spin orientation in response to the applied magnetic field. For the interpretation of the experimental observations, we perform ab initio calculations by means of the Korringa-Kohn-Rostoker Green's function method. The calculations demonstrate that the Cr-tip is not a perfect antiferromagnet and has an uncompensated magnetic moment which changes its spin orientation continuously due to the applied magnetic field.

  18. 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:

  19. From the Inside Out: An Organizational View of Electronic Resources and Collection Development.

    Science.gov (United States)

    Younger, Jennifer A.

    2002-01-01

    Discusses electronic resources and collection development. Topics include how electronic resources are changing the world of access to information; how and why scholars and research libraries use electronic resources; digitization initiatives; knowledge and learning via the Web; archiving electronic resources; and building collections versus…

  20. Nuclear and electronic resonance spectroscopy of single molecules by radio-frequency scanning tunnelling microscopy

    OpenAIRE

    Müllegger, Stefan; Tebi, Stefano; Das, Amal K.; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

    2014-01-01

    The ongoing miniaturization in nanoscience and -technology challenges the sensitivity and selectivity of experimental analysis methods to the ultimate level of single atoms and molecules. A promising new approach, addressed here, focuses on the combination of two well-established complementary techniques that have proven to be very successful in their own fields: (i) low-temperature scanning tunneling microscopy (STM), offering high spatial resolution for imaging and spectro...

  1. Temperature dependence of the recombination fluorescence of photoionized indole and N,N,N',N'-tetramethyl-p-phenylenediamine in organic glasses. Consequences of electron tunneling and diffusion

    International Nuclear Information System (INIS)

    The recombination fluorescence seen when TMPD is photoionized in methylcyclohexane, 3-methylhexane, and 2-methyltetrahydrofuran glasses and when indole is photoionized in 2-propanol and ethanol glasses has been investigated. The initial intensity and decay rate of the recombination fluorescence decreases as the UV irradiation temperature is increased from temperatures below the glass transition temperature T/sub g/ of the matrix. This is interpreted in terms of electron tunneling to the cation in which the tunneling barrier height or electron trap depth increases slightly (0.05 to 0.2 eV) with increasing irradiation temperature. By considering how the matrix polarity affects the degree of electron trap deepening as well as the electron trap depth relative to the excited singlet level of the solute, we are able to understand the difference in magnitudes and their changes for the initial decay rate and the initial recombination fluorescence. At temperatures 10 to 30 K above T/sub g/, depending on the matrix polarity, diffusive recombination dominates tunneling recombination and produces a peak in the recombination fluorescence unless the electron trap depth has dropped below the excited singlet of the solute. Thus, this type of experiment offers a simple diagnostic for distinguishing tunneling and diffusive recombination of electrons with cations in disordered matrices

  2. Carrier-envelope phase-dependent electron tunneling in a coupled double-quantum-dot system driven by a few-cycle laser pulse

    International Nuclear Information System (INIS)

    We theoretically investigate the dependence of the electron tunneling on the carrier-envelope phase of a few-cycle laser pulse in a coupled double-quantum-dot system, and we show that the electron tunneling between coupled quantum dots is very sensitive to the carrier-envelope phase under a change of the parameters of the system. This in turn provides an additional means to measure the carrier-envelope phase of a laser pulse at lower laser intensity regime in the solid-state nanostructure.

  3. Organization of adenine on Ag(111) and correlated interfacial electronic structure measured with low temperature scanning tunneling microscopy

    Science.gov (United States)

    Pearl, Thomas P.; Andrews, Katie M.; Davis, Bryce F.

    2010-03-01

    Low temperature scanning tunneling microscopy and spectroscopy has been used to observe the organization of the nucleobase adenine on the Ag(111) surface as well as to resolve modifications to Ag(111) surface electronic structure. Multiple hydrogen bonding interactions between adenine adsorbates dictate the formation of dimers on the surface as well as long range order of molecular domains, which have limited commensuration with the Ag(111) lattice. Differential conductance spectroscopy recorded at 15 K reveals an upward energetic shift of the Shockley-type surface state native to Ag(111) from a band edge of -67 meV on the clean surface to+82.5 meV recorded over adenine islands. Differential conductance maps show free-electron like scattering in the adenine domains. Dispersion of the parallel wave vector of scattered electrons in the adenine domains is compared to the dispersion for electron scattering in bare silver and the ratio of effective masses for electrons in those bands is 1.1 ± 0.05. It is hypothesized that this shift occurs due to a combination of effects brought on by the adsorption of adenine including changes in work function and dipole-induced screening of the first image potential.

  4. 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…

  5. Use of Electronic Resources in Degree College Libraries in Chandigarh

    Directory of Open Access Journals (Sweden)

    Jaspal Kaur Bhatia

    2011-11-01

    Full Text Available The electronic resources (e-resources available in a library play a prominent role in facilitating access to required information to the users in an easy and expeditious manner. The e-resources, like CD-ROM databases, online journals, online books, OPACs, and the internet, are slowly replacing the importance and usage of print media. A study of 11 degree colleges in Chandigarh, which have students and teachers strength of over 30000, was conducted. For the purpose of the study, a sample selected was 770 which included 60 students and 10 teachers from each of the colleges, respectively. The objectives of this study was to know the usage of e-resources and services by the users of degree college libraries in Chandigarh; find out the impediments encountered by the users while accessing and using the e-resources; and suggest measures to take full advantage of IT to make degree college libraries more digitally resourceful and for providing information services data from the users.teachers and students.to know the impact of e-resources. The data collected was analysed using simple percentage technique.

  6. The Superluminal Tunneling Story

    CERN Document Server

    Aichmann, Horst

    2013-01-01

    Since 1992 experimental evidence of superluminal (faster than light, FTL) signals are causing much excitement in the physical community and in the media. Superluminal signal velocity and zero time tunneling was first observed in an analog tunneling experiment with microwaves. Recently, the conjectured zero time of electron was claimed to be observed in ionizing helium. The FTL signal velocity was reproduced with infrared light and with various tunneling barriers in several laboratories worldwide. Remarkable, it was shown that the tunneling time is a universal quantity for elastic and for electromagnetic fields. Many theoretical physicists predicted this FTL nature of the tunneling process. However, even with this background many members of the physics community did not accept the superluminal signal velocity interpretation of the experimental results and they also ignored the universal tunneling time. The predicted and measured zero tunneling time was taken as a fantastic nonsense. A brief explanation of the ...

  7. 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.

  8. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared with the molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new app...

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

    Energy Technology Data Exchange (ETDEWEB)

    Weng, Q. C.; Zhu, Z. Q. [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241 (China); An, Z. H., E-mail: anzhenghua@fudan.edu.cn [State Key Laboratory of Surface Physics and Institute of Advanced Materials, Fudan University, Shanghai 200433 (China); Song, J. D.; Choi, W. J. [Center for Opto-Electronic Convergence Systems, Institute of Science and Technology, Seoul 130-650 (Korea, Republic of)

    2014-02-03

    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 10{sup 4} photons/s for sensitive imaging applications by keeping the device far from saturation by employing an appropriate reset frequency.

  10. Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs

    International Nuclear Information System (INIS)

    Polycrystalline Ce1-xLaxRhAs is investigated by means of break-junction tunneling. On Ce substituted by La (x=0.01), a pronounced hump structure is developed at the bias +/-0.25V with a shallow dip on it. The hump emergence is consistent with a drastic reduction in the resistivity. These facts give direct evidence for the appearance of mid-gap states near the Fermi energy by a small La substitution for Ce in CeRhAs

  11. 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

  12. The Superluminal Tunneling Story

    OpenAIRE

    Aichmann, Horst; Nimtz, Günter

    2013-01-01

    Since 1992 experimental evidence of superluminal (faster than light, FTL) signals are causing much excitement in the physical community and in the media. Superluminal signal velocity and zero time tunneling was first observed in an analog tunneling experiment with microwaves. Recently, the conjectured zero time of electron was claimed to be observed in ionizing helium. The FTL signal velocity was reproduced with infrared light and with various tunneling barriers in several l...

  13. Journals, Data and Abstracts Make an Integrated Electronic Resource

    Science.gov (United States)

    Boyce, P.

    1996-12-01

    Astronomy now has an integrated, Web-based information resource for research papers, data and bibliographic information. The major scholarly research journals, a comprehensive abstract service and the astronomical data centers are now linked together to provide an information resource which is not available to most other scientific disciplines. As of January, 1997, the Astrophysical Journal joins the ApJ Letters on the Web. Astronomy and Astrophysics Supplements now has a page image version. Elsevier's electronic journal New Astronomy has recently made its appearance. Over forty percent of the new peer-reviewed, astronomical literature is now available electronically. The main Astronomy and Astrophysics journal, the Astronomical Journal and others will be available by 1998, at which point ninety percent of the literature will be available electronically, a figure not approached by any other scientific discipline. With so many different sources, one of the challenges has been to integrate the on-line, peer-reviewed literature into a resource which serves the astronomical community in a unified and coherent manner. Following the lead of the AAS, the major publishers have chosen to rely upon the NASA-supported Astrophysics Data System (ADS) and the astronomical data centers to provide the means by which the various separate journals can interoperate. The data centers and the ADS have developed unique identification codes for journal articles. By adopting the existing standard "bibcodes" and integrating them into their WWW links, each of the major astronomical journals are able to link to the abstracts of most of the referenced articles. Since the ADS also serves as an on-line repository for page images of the past twenty years of the major astronomical journals, the full text of many of the referenced articles are available, too. The articles in the ADS have recently been linked through their references, both forward and backward in time. With the "bibcode" providing the linking framework, papers in the electronic research journals, data and abstracts will be incorporated into the system in a routine manner. The astronomical community now has an ever-growing, operational integrated information system which fulfills today, the dream of the digital library. It remains to be seen how this electronic resource will affect the progress of research.

  14. 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 < 0, and I = 0 near V = 0 for an either n- or p-nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V < 0 for an n-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.

  15. Electron immigration from shallow traps to deep traps by tunnel mechanism on Seydisehir aluminas

    International Nuclear Information System (INIS)

    In this study, the fading mechanism of Seydisehir alumina in Turkey, which is considered to be used for radiation dosimetric purposes, was investigated. The materials were first exposed to beta radiation and then stored in dark and dry ambient conditions at room temperature (RT) at previously desired storage periods. It was observed that the glow curve of Seydisehir alumina consists of four glow peaks between RT and 400 deg. C. The glow peaks (peaks 1, 2 and 3) between room temperature and 250 deg. C possessed very high levels of anomalous fading. However, the intensity of new glow peak at around 378 deg. C is highly increased with time. As a result of the experimental studies, it was concluded that the reason behind anomalous fading can be explained by means of tunneling (quantum tunneling) mechanism. - Highlights: ? Fading mechanism of Turkish Seydisehir alumina was investigated. ? Materials were exposed to beta radiation and stored under special conditions. ? Glow curve was obtained and changes have been observed.

  16. Excess electrons scavenging in n-dodecane solution: The role of tunneling of electron from its localized state to acceptor

    Energy Technology Data Exchange (ETDEWEB)

    Borovkov, Vsevolod I. [Institute of Chemical Kinetics and Combustion of SB RAS, ul. Institutskaya, 3, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, ul. Pirogova, 2, Novosibirsk 630090 (Russian Federation)], E-mail: borovkov@kinetics.nsc.ru

    2008-10-15

    The quenching of delayed radiofluorescence of n-dodecane solutions of N,N,N',N'-tetramethyl-1,4-phenylenediamine by both electron acceptors and electric field was studied. The values of excess electron mobility and rate constants of electron scavenging by different acceptors were determined over the temperature range of 265-343 K. The data were analyzed with the theory of diffusion-controlled reactions with distant transfer of electron to an acceptor. Evidence was obtained that no enthalpy and entropy of activation were needed for the electron scavenging.

  17. 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

  18. Effect of inelastic electron-phonon interaction on tunneling magnetoresistance through ferromagnetic-organic molecule-ferromagnetic junction

    Science.gov (United States)

    Ashhadi, M.; Ketabi, S. A.

    2011-09-01

    We have studied the effect of inelastic electron-phonon interaction on the spin-dependent transport properties of a molecule, trans-polyacetylene ( trans-PA), as a molecular bridge sandwiched between two ferromagnetic (FM) electrodes. The work is based on a tight-binding Hamiltonian model within the framework of a generalized Green's function technique and relies on the Landauer-Büttiker formalism as the basis for studying the current-voltage characteristic of this system. We use the wide-band approximation for FM electrodes. It is shown that due to inelastic interactions, the spin currents increase in a finite value of voltage and tunnel magnetoresistance (TMR) decreases compared with TMR obtained in the absence of phonons.

  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. 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

  1. Hot-Electron Tunneling sensors for high-resolution x-ray and gamma-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mears, C.A.; Labov, S.E.; Frank, M.; Netel, H.

    1997-02-07

    Over the past 2 years, we have been studying the use of Hot Electron Tunneling sensors for use in high-energy-resolution x-ray and gamma-ray spectrometers. These sensors promise several advantages over existing cryogenic sensors, including simultaneous high count rate and high resolution capability, and relative ease of use. Using simple shadow mask lithography, we verified the basic principles of operation of these devices and discovered new physics in their thermal behavior as a function applied voltage bias. We also began to develop ways to use this new sensor in practical x-ray and gamma-ray detectors based on superconducting absorbers. This requires the use of quasiparticle trapping to concentrate the signal in the sensing elements.

  2. Investigation of Gd3N@C2n (40 < n < 44) family by Raman and inelastic electron tunneling spectroscopy

    CERN Document Server

    Burke, Brian G; Williams, Keith A; Ge, Jiechao; Shu, Chunying; Fu, Wujun; Dorn, Harry C; Kushmerick, James G; Puretzky, Alexander A; Geohegan, David B

    2009-01-01

    The structure and vibrational spectrum of Gd3N@C80 is studied through Raman and inelastic electron tunneling spectroscopy (IETS) as well as density functional theory (DFT) and universal force field (UFF) calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd3N-C80 bond which reduces the ideal icosahedral symmetry of the C80 cage. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the Gd3N@C2n (40 < n < 44) family as well as Y3N@C80, Lu3N@C80, and Y3N@C88 for comparison. Conductance measurements have been performed on Gd3N@C80 and reveal a Kondo effect similar to that observed in C60.

  3. Tunneling of Conduction Band Electrons Driven by a Laser Field in a Double Quantum dot: An Open Systems Approach

    Science.gov (United States)

    Ahmadi, B.; Salimi, S.; Khorashad, A. S.

    2015-08-01

    In this paper, we investigate tunneling of conduction band electrons in a system of an asymmetric double quantum dot which interacts with an environment. First we consider the case in which the system only interacts with the environment and demonstrate that as time goes to infinity they both reach an equilibrium, which is expected, and there is always a maximum and minimum for the populations of the states of the system. Then we investigate the case in which an external resonant optical pulse (a laser) is applied to the system interacting with the environment. However, in this case for different intensities we have different populations of the states in equilibrium and as the intensity of the laser gets stronger, the populations of the states in equilibrium approach the same constant.

  4. 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...

  5. 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 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.

  6. Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical Gauge fields

    Science.gov (United States)

    Bermudez, Alejandro; Porras, Diego

    2015-10-01

    We introduce a scheme that combines photon-assisted tunneling (PAT) by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t\\gg J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the PAT scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field.

  7. 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

    2014-11-01

    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 Au144 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 Au144-MPCs and EC-STS experiments with laterally separated individual Au144-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 Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles.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 Au144 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 Au144-MPCs and EC-STS experiments with laterally separated individual Au144-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 Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03793f

  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 collections ...

  9. Si/SiGe electron resonant tunneling diodes with graded spacer wells

    International Nuclear Information System (INIS)

    Resonant tunneling diodes have been fabricated using graded Si1-xGex (x=0.3->0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the peak current density is achieved. Peak current densities of 0.08A/cm2 with peak-to-valley current ratios of 1.67 have been achieved for a low peak voltage of 40 mV at 77 K. This represents an improvement of over an order of magnitude compared to previous work. [copyright] 2001 American Institute of Physics

  10. 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 electr...

  11. 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…

  12. Systematic modulation of quantum (electron) tunneling behavior by atomic layer deposition on nanoparticulate SnO2 and TiO2 photoanodes.

    Science.gov (United States)

    Prasittichai, Chaiya; Avila, Jason R; Farha, Omar K; Hupp, Joseph T

    2013-11-01

    Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3(-). Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes. PMID:24148005

  13. 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.

  14. Electronic disorder of P- and B-doped Si at the metal–insulator transition investigated by scanning tunnelling microscopy and electronic transport

    International Nuclear Information System (INIS)

    The (111)-2 × 1 surface of in situ cleaved heavily P- or B-doped Si is investigated by scanning tunnelling microscopy and spectroscopy at room temperature and at low temperature. P atoms have been identified on different sites of the Si(111)-2 × 1 surface by their characteristic voltage-dependent contrast for positive as well as negative buckling of the ?-bonded chains. The distributions of dopants per surface area and of nearest-neighbour distances are found to be in agreement with a random arrangement of dopants in Si up to doping levels well above the metal–insulator transition. In addition, P atoms have been identified by their depth-dependent contrast down to the third layer beneath the surface with a volume density in agreement with the bulk doping density. The random electronic disorder supports the view of an Anderson transition driven by disorder close to the critical concentration or critical uniaxial stress. (paper)

  15. 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.

  16. Approach to surface structure determination with the scanning tunneling microscope: Multiple-gap imaging and electron-scattering quantum-chemistry theory

    International Nuclear Information System (INIS)

    We have successfully developed and tested a method of quantitative surface structure determination using scanning tunneling microscopy (STM). Image simulations of the c(2x2) S on Mo(100) chemisorption system were calculated as a function of surface and tip structure using electron-scattering quantum-chemistry STM theory. STM images with a wide range of tunneling gap resistance values were acquired in a ''multiple-gap'' mode which preserves information on the z separation and lateral registry between the images under different tunneling conditions. The best fit of a numerical comparison of the image simulations with experimental data simultaneously determined two structural parameters of the surface. The STM results differ from those of dynamical LEED by approximately 0.1 A, which we estimate to be the level of accuracy obtainable with the present implementation of the method

  17. 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.

  18. Electron tunneling studies of spin-flip scattering with native and artificial rare-earth barriers

    International Nuclear Information System (INIS)

    Both artificial and native rare earth (RE) tunnel barriers have been successfully fabricated. Artificial barriers are of the form M-REOx-M (M = Al, Pb, PbBi; RE = Ho, Dy, Gd, Lu), and native barriers are of the form RE-REOx-s (S = Pb, PbBi; RE = Dy, Ho). Artificial barriers are formed by oxidizing a thin (5-20 angstrom) film of evaporated RE. Current-Voltage characteristics (I-V) produced by Al-REOx-Al junctions shown substantial gap depression and gap smearing for magnetic rare earths (Ho, Dy, Gd). Using the Abrikosov-Gorkov (AG) theory of spin-flip scattering, we have successfully fit gap-depressed I-V's. Since the actual experimental temperature (T = 0.93 degree K) corresponds to a high reduced temperature (T/Tc) for Al, the AG predicted temperature dependence of the pair potential was necessary to obtain good fits. Our tunneling experiments utilize a variety of fabrication geometries. Our results do not support the view that contact between Al and the REOx barrier is responsible for gap depression. Instead, they indicate that gap depression is caused by inter-diffusion of Al and RE at the metal-metal interface. Native Dy barriers have been fabricated in-situ using a wet-oxygen ambient. The presence of water was found to be crucial for the formation of low leakage (0.6%) barriers. PbBi counter-electrodes show no sign-of-gap depression, despite clean contact with the DyOx barriers. Barrier characteristics for native RE barriers are quite different from those of artificial RE barriers. Native RE dV/dI's are quite symmetric corresponding to rectangular (flat) WKB barriers. The average height and width are 1.02 eV and 27.8 A, respectively. IETS has been performed for both HoOx and DyOx barriers. We report new quantitative results for barrier phonons in both HoOx and DyOx

  19. 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...

  20. 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: 4.772, year: 2014

  1. 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.

  2. 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.? ?????? ?????? ?????????? ??????????? ????????? ???????? ??????????? ?????????, ????????? ? ???? ? ???????? ???????? ??????????? ????????????? ????????. ???????? ???????????? ?????????? ??????????? ???????? ???????? ????????????? ????????, ??????? ?? ??????????, ????????? ????????, ?????? ?? ??????????????, ?????????? ?????????, ???????????? ????????? ?? ???????????? ???????? ????????; ???? ? ??????? ????????? ? ????????? ? ?????????? ?????????? ??????????. ?? ????? ???????????? ? ???????????? ???????? ??????????? ????????? ?????? ???? ??????????? ?????????? ???????????, ????????? ? ??????, ? ????: ????? ?????????? ???????? ???????? ????????????? ????????; ????? ???????????? ? ???????? ?????????? ? ???????????? ????????? ?????????? ????, ????????? ??????????.

  3. Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

    DEFF Research Database (Denmark)

    Chi, Qijin; Farver, O

    2005-01-01

    A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 angstrom(-1) in H2O and D2O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximate to 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism

  4. 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.

  5. Effects of Electronic Information Resources Skills Training for Lecturers on Pedagogical Practices and Research Productivity

    Science.gov (United States)

    Bhukuvhani, Crispen; Chiparausha, Blessing; Zuvalinyenga, Dorcas

    2012-01-01

    Lecturers use various electronic resources at different frequencies. The university library's information literacy skills workshops and seminars are the main sources of knowledge of accessing electronic resources. The use of electronic resources can be said to have positively affected lecturers' pedagogical practices and their work in general. The…

  6. 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.

  7. 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

    International Nuclear Information System (INIS)

    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

  8. 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

    Energy Technology Data Exchange (ETDEWEB)

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M., E-mail: champ@neu.edu [Department of Physics and Center for Interdisciplinary Research on Complex Systems,Northeastern University, Boston, Massachusetts 02115 (United States)

    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.

  9. 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

  10. The Dwell Time of Electron Tunneling Through a Double Barrier in the Presence of Rashba SOI

    International Nuclear Information System (INIS)

    Some aspects related to the influence of the Rashba spin-orbit interaction (SOI) on the dwell time spent by the electrons in an asymmetric double barrier are analyzed. It is revealed that in the presence of the Rashba SOI, a difference between the dwell times associated to the spin-up and spin-down species can be obtained. This opens the way to a spin filtration in the time domain.

  11. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C.

    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 ...

  12. Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

    DEFF Research Database (Denmark)

    Chi, Qijin; Farver, O; Ulstrup, Jens

    2005-01-01

    A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites i...

  13. In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy

    OpenAIRE

    Sanduijav B; Matei DG; Springholz G.

    2010-01-01

    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 ...

  14. 21 October 2008 - LHC Inauguration - Deputy Minister for Environment, Physical Planning and Public Works T. Xanthopulos welcomed by CERN Director-General R. Aymar, visiting the ATLAS cavern and LHC tunnel and signing the electronic guest book with E. Tsesmelis.

    CERN Multimedia

    CERN Photo Service

    2008-01-01

    21 October 2008 - LHC Inauguration - Deputy Minister for Environment, Physical Planning and Public Works T. Xanthopulos welcomed by CERN Director-General R. Aymar, visiting the ATLAS cavern and LHC tunnel and signing the electronic guest book with E. Tsesmelis.

  15. Electronic energy levels, wavefunctions and potential landscape of nanostructures probed by magneto-tunnelling spectroscopy

    International Nuclear Information System (INIS)

    We create electrostatically induced quantum dots by thermal diffusion of interstitial Mn out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This leads to the formation of deep, approximately circular and strongly confined dot-like potential minima in a large mesa diode structure. The minima are formed without need for advanced lithography or electrostatic gating. Using fields of up to 30 T, magnetotunnelling spectroscopy of an individual dot reveals the symmetry of the electronic eigenfunctions and, for the approximately circular dots, a rich spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| ranging from 0 up to 11. We find that a small fraction of the dots has elongated potential minima, giving rise to quenching of the orbital angular momentum of the electronic eigenstates. By developing a model to describe the diffusion of the Mn interstitial ions, we determine the electrostatic potential landscape in the quantum well and hence the distribution of dot shapes and sizes. This is in a good agreement with our experimental data.

  16. 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.

  17. eFG: an electronic resource for Fusarium graminearum.

    Science.gov (United States)

    Liu, Xiaoping; Zhang, Xiaodong; Tang, Wei-Hua; Chen, Luonan; Zhao, Xing-Ming

    2013-01-01

    Fusarium graminearum is a plant pathogen, which causes crop diseases and further leads to huge economic damage worldwide in past decades. Recently, the accumulation of different types of molecular data provides insights into the pathogenic mechanism of F. graminearum, and might help develop efficient strategies to combat this destructive fungus. Unfortunately, most available molecular data related to F. graminearum are distributed in various media, where each single source only provides limited information on the complex biological systems of the fungus. In this work, we present a comprehensive database, namely eFG (Electronic resource for Fusarium graminearum), to the community for further understanding this destructive pathogen. In particular, a large amount of functional genomics data generated by our group is deposited in eFG, including protein subcellular localizations, protein-protein interactions and orthologous genes in other model organisms. This valuable knowledge can not only help to disclose the molecular underpinnings of pathogenesis of the destructive fungus F. graminearum but also help the community to develop efficient strategies to combat this pathogen. To our best knowledge, eFG is the most comprehensive functional genomics database for F. graminearum until now. The eFG database is freely accessible at http://csb.shu.edu.cn/efg/ with a user-friendly and interactive interface, and all data can be downloaded freely. DATABASE URL: http://csb.shu.edu.cn/efg/ PMID:23798489

  18. 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.

  19. XPS and electron transport study of the paramagnetic dusting effect on MgO-based magnetic tunnel junctions

    Science.gov (United States)

    Kim, Dongseok; Kim, Jonghyun; Jung, K. Y.; Jang, Youngjae; Rhie, Kungwon; Lee, B. C.; Joo, Sungjung; Kang, H. J.; Chae, Hong-Chol

    2015-09-01

    Amorphous FeZr was dusted in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), and the effects on tunnel phenomena were investigated. As the thickness of the FeZr layer between the CoFeB and the MgO layers increased, the resistance increased rapidly and the bias dependence became asymmetric while the tunneling magneto-resistance (TMR) decreased. The interface was investigated by using X-ray photoemission spectroscopy, and the change in the transport property due to dusting was explained.

  20. Assessing Ongoing Electronic Resource Purchases: Linking Tools to Synchronize Staff Workflows

    Science.gov (United States)

    Carroll, Jeffrey D.; Major, Colleen; O'Neal, Nada; Tofanelli, John

    2012-01-01

    Ongoing electronic resource purchases represent a substantial proportion of collections budgets. Recognizing the necessity of systematic ongoing assessment with full selector engagement, Columbia University Libraries appointed an Electronic Resources Assessment Working Group to promote the inclusion of such resources within our current culture of…

  1. ????????????????????--?????????????? | Electronic Resource Sharing of Public Libraries in Taiwan

    Directory of Open Access Journals (Sweden)

    ??? Li-Hsiang Lai

    2001-04-01

    Full Text Available

    ???85-97

    ?????????????????????88???????????????????????????????????????????????????????????????????????www???????????????????????????????????????????????????????????????

    ??????????????????????????????????????????????????????????????????????????????????????????????

    The Project of Electronic Resource Sharing of Public Libraries in Taiwan was subsidized by Ministry of Education and carried out by National Taichung Library. The Project started in January of 1999. Its purposes are to establish an electronic database system through WWW for all the public libraries in Taiwan to provide the public to use, and to form a public library cooperation mechanism to foster resource sharing among the libraries.

    This paper introduces the brief history, current status, and achievement o

  2. Superluminal Tunneling Devices

    CERN Document Server

    Nimtz, G

    2002-01-01

    Photonic tunneling permits superluminal signal transmission. The principle of causality is not violated but the time duration between cause and effect can be shortened compared with an interaction exchange with velocity of light. This outstanding property can be applied to speed-up photonic signal modulation and transmission as well as to improve micro-electronic devices. Superluminal photonic signal transmission have been presented at microwave and infrared frequencies already. Presumably superluminal photonic and electronic devices can become reality having in mind the experimental evidence of the universal tunneling time of photons and of electrons.

  3. 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...

  4. User Perception of Electronic Resources in the University of Ilorin, Nigeria (UNILORIN)

    OpenAIRE

    BASHORUN; M. Tunji; ISAH Abdulmumin; M.Y ADISA

    2011-01-01

    This study examined the user perception of the electronic resources by the academic staff of the University of Ilorin. The sample consists of 250 academic staff selected from eight (8) out of the twelve (12) faculties that made up of the university. Data were collected through an electronic resources user perceptional survey (ERUPS). Responses were received from 225 (90%) academic staff of the eight faculties. Analysis revealed frequency of use of electronic resources was low. Reasons alluded...

  5. 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.

  6. Availability And Use Of Electronic Resources In Spspm Libraries: A Study

    OpenAIRE

    Kamble M.G; Ghante P. B.

    2012-01-01

    This research paper describes availability and use of electronic resource by faculty members of SPSPM libraries. Now a day's e - resources are growing tremendously in the world and demands of the same are also increasing day by day from users.

  7. Resonance tunneling spectroscopy of heteropoly compounds

    Science.gov (United States)

    Dalidchik, F. I.; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A.

    2012-12-01

    The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

  8. Resonance tunneling spectroscopy of heteropoly compounds

    Energy Technology Data Exchange (ETDEWEB)

    Dalidchik, F. I., E-mail: domfdal@mail.ru; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A. [Russian Academy of Sciences, Semenov Institute of Chemical Physics (Russian Federation)

    2012-12-15

    The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

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

    OpenAIRE

    Zhong Wenjuan; Wu Xuezhi; Zhao Tieqin

    2014-01-01

    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 resource...

  10. 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…

  11. Impact of adsorbed organic monolayers on vacuum electron tunneling contributions to electrical resistance at an asperity contact

    Science.gov (United States)

    Berman, Diana; Walker, Matthew; Krim, Jacqueline

    2012-02-01

    Electrical Contact Resistance measurements are reported for RF MEMS switches situated within an ultrahigh vacuum system equipped with in situ oxygen plasma cleaning capabilities. Measurements were preformed on Au/Au permanently adhered switches, and functioning Au/RuO2 switches in the presence and absence of adsorbed monolayers of pentane and dodecane. The data are analyzed to explore how adsorbed molecules in regions close to the contact may impact vacuum tunneling contributions to the experimentally measured resistance: (1) The resistance associated with direct contact in parallel with a vacuum tunneling path, which upon uptake of the monolayer is replaced by the molecular resistance, and (2) A series connection of the direct contact resistance with the molecular layer after adsorption occurs, with the vacuum tunneling path assumed to be negligible. The results favor scenario (1), whereby uptake of the molecular layer effectively shuts down the vacuum tunneling path, which in this case is effectively ˜30 Ohms in the absence of an adsorbed film. The methods constitute a new and original approach to documenting vacuum tunneling levels in regions of close proximity. Funding agencies: NSF, AFOSR MURI, DARPA. [4pt] [1] D. Berman, M. Walker, C. Nordquist, J. Krim, J. Appl. Phys., in press

  12. Attosecond tunnelling interferometry

    Science.gov (United States)

    Pedatzur, O.; Orenstein, G.; Serbinenko, V.; Soifer, H.; Bruner, B. D.; Uzan, A. J.; Brambila, D. S.; Harvey, A. G.; Torlina, L.; Morales, F.; Smirnova, O.; Dudovich, N.

    2015-10-01

    Attosecond physics offers new insights into ultrafast quantum phenomena involving electron dynamics on the fastest measurable timescales. The rapid progress in this field enables us to re-visit one of the most fundamental strong-field phenomena: field-induced tunnel ionization. In this work, we employ high-harmonic generation to probe the electron wavefunction during field-induced tunnelling through a potential barrier. By using a combination of strong and weak driving laser fields, we modulate the atomic potential barrier on optical subcycle timescales. This induces a temporal interferometer between attosecond bursts originating from consecutive laser half-cycles. Our study provides direct insight into the basic properties of field-induced tunnelling, following the evolution of the electronic wavefunction within a temporal window of approximately 200 attoseconds.

  13. 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.

  14. Issues in Electronic Resource Services in K-12 School Library Settings.

    Science.gov (United States)

    Farmer, Leslie S. J.

    2002-01-01

    Discusses the unique factors that online electronic resources pose in school library settings. Topics include the appropriateness of online electronic resources; strategic planning for Internet access, including acceptable use policies; administrative issues; selection and acquisition; organization; and intellectual access, including library…

  15. Checklist Manifesto for Electronic Resources: Getting Ready for the Fiscal Year and Beyond

    Science.gov (United States)

    England, Lenore; Fu, Li; Miller, Stephen

    2011-01-01

    Organization of electronic resources workflow is critical in the increasingly complicated and complex world of library management. A simple organizational tool that can be readily applied to electronic resources management (ERM) is the use of checklists. Based on the principles discussed in The Checklist Manifesto: How to Get Things Right, the…

  16. What Do Libraries Really Do with Electronic Resources? The Practice in 2003

    Science.gov (United States)

    Shorten, Jay

    2005-01-01

    One hundred fourteen academic libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, electronic resources, subject guides, ready reference, and their own catalogue both on their home page and within their…

  17. Using a Decision Grid Process to Build Consensus in Electronic Resources Cancellation Decisions

    Science.gov (United States)

    Foudy, Gerri; McManus, Alesia

    2005-01-01

    Many libraries are expending an increasing part of their collections budgets on electronic resources. At the same time many libraries, especially those which are state funded, face diminishing budgets and high rates of inflation for serials subscriptions in all formats, including electronic resources. Therefore, many libraries need to develop ways…

  18. 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.

  19. Developing Humanities Collections in the Digital Age: Exploring Humanities Faculty Engagement with Electronic and Print Resources

    Science.gov (United States)

    Kachaluba, Sarah Buck; Brady, Jessica Evans; Critten, Jessica

    2014-01-01

    This article is based on quantitative and qualitative research examining humanities scholars' understandings of the advantages and disadvantages of print versus electronic information resources. It explores how humanities' faculty members at Florida State University (FSU) use print and electronic resources, as well as how they perceive these…

  20. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    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{endash}Nordheim tunneling barriers ({Phi}{sub 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{endash}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 10{sup 18}{endash}10{sup 20}cm{sup {minus}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 American Institute of Physics.

  2. 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.

  3. 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 American Institute of Physics

  4. LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Radiatively and tunnel-coupled surface electromagnetic waves in metal — dielectric structures

    Science.gov (United States)

    Lyndin, N. M.; Svetikov, V. V.; Sychugov, V. A.; Usievich, B. A.; Yakovlev, V. A.

    1999-09-01

    The surface electromagnetic modes in five-layer metal — dielectric structures are investigated by a numerical computational method. The existence of two types of plasmon modes — radiatively and tunnel-coupled — is demonstrated. The mode type is determined by the specific geometry of the structure. The results of estimates of the effective refractive index of the plasmon leaky mode excited in an asymmetric three-layer metal — dielectric structure, are presented. The optical transparency effect, arising on excitation of the tunnel-coupled surface electromagnetic waves, is demonstrated experimentally.

  5. 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

  6. 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

    OpenAIRE

    Gärtner, Stefan; Fiedler, Benjamin; Bauer, Oliver; Marele, Antonela; Sokolowski, Moritz M

    2014-01-01

    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?2)R45° – 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4?2 × 5?2)R45° 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 ...

  7. Preliminary Performance Data on General Electric Integrated Electronic Control Operating on J47 RX1-3 Turbojet Engine in NACA Altitude Wind Tunnel

    Science.gov (United States)

    Blivas, Darnold; Taylor, Burt L., III

    1950-01-01

    Performance data obtained with recording oscillographs are presented to show the transient response of the General Electric Integrated Electronic Control operating on the J47 RXl-3 turbo-Jet engine over a range of altitudes from 10,000 to 45,000 feet and at ram pressure ratios of 1.03 and 1.4. These data represent the performance of the final control configuration developed after an investigation of the engine transient behavior in the NACA altitude wind tunnel. Oscillograph traces of controlled accelerations (throttle bursts),oontrolled decelerations (throttle chops), and controlled altitude starts are presented.

  8. 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

  9. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloys as magnetic electrodes

    International Nuclear Information System (INIS)

    High resolution transmission electron microscopy, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe(13 nm)/Al2O3(3 nm)/Co(13 nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film. The large Co concentration in the Al2O3 interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates. - Highlights: • Tunnel magnetic junctions have been grown on different substrates. • Their nanoscale structure has been studied and compared to the magnetic properties. • Inter-diffusion to the tunnel barrier has been observed. • Differences between tunnel junctions have a direct impact on magnetic properties

  10. 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...

  11. Electron beam pasteurised oil palm waste: a potential feed resource

    International Nuclear Information System (INIS)

    Pasteurization of oil palm empty fruit bunch (EFB) was performed using electron beam single sided irradiation. The dose profiles of oil palm EFB samples for different thickness in both directions X and Y were established. The results showed the usual characteristics dose uniformity as sample thickness decreased. The mean average absorbed dose on both sides at the surface and bottom of the samples for different thickness samples lead to establishing depth dose curve. Based on depth dose curve and operation conditions of electron beam machine, the process throughput for pasteurized oil palm EFB were estimated. (Author)

  12. Simulation of electron transmittance and tunnel current in n{sup +} Poly-Si/HfSiO{sub x}N/Trap/SiO{sub 2}/Si(100) capacitors using analytical and numerical approaches

    Energy Technology Data Exchange (ETDEWEB)

    Noor, Fatimah A., E-mail: fatimah@fi.itb.ac.id; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal [Physics of Electronic Materials Research Division Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2015-04-16

    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 HfSiO{sub x}N/SiO{sub 2} dual ultrathin layer is used as the gate oxide in an n{sup +} poly- Si/oxide/Si capacitor to replace SiO{sub 2}. The main problem of using HfSiO{sub x}N is the charge trapping formed at the HfSiO{sub x}N/SiO{sub 2} 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 HfSiO{sub x}N/SiO{sub 2} interface in the electron transmittance and tunneling current. The transmittance and tunneling current in n{sup +} poly- Si/HfSiO{sub x}N/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.

  13. Resources

    Science.gov (United States)

    ... palate - resources Colon cancer - resources Cystic fibrosis - resources Depression - resources Diabetes - resources Digestive disease - resources Drug abuse - resources Eating disorders - resources Elder care - resources Epilepsy - resources Family ...

  14. Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Useinov, N.Kh., E-mail: Niazbeck.Useinov@kpfu.ru; Petukhov, D.A.; Tagirov, L.R.

    2015-01-01

    The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown.

  15. Longitudinal-optical-phonon assisted tunneling in tunneling bi-quantum well structures

    Science.gov (United States)

    Muto, Shunichi; Inata, Tsuguo; Tackeuchi, Atsushi; Sugiyama, Yoshihiro; Fujii, Toshio

    1991-05-01

    This paper discusses the electron tunneling time observed in a new AlGaAs/GaAs superlattice structure, the tunneling bi-quantum well (TBQ). To calculate the nonresonant tunneling time, experiments were conducted on resonant tunneling, to confirm that the 60-percent rule of conduction-band discontinuity accurately evaluates the free tunneling probability of electrons. It was found that the observed recovery time agrees quite well with the calculated longitudinal optical phonon emission tunneling time for thin (not greater than 10 monolayers) barriers.

  16. 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…

  17. Use and Users of Electronic Library Resources: An Overview and Analysis of Recent Research Studies

    Science.gov (United States)

    Tenopir, Carol

    2003-01-01

    This Council on Library and Information Resources (CLIR) report summarizes and analyzes more than 200 recent research publications that focus on the use of electronic library resources (digital libraries and digital resources) and were published between 1995 and 2003. Eight major ongoing studies (each with multiple publications) are identified as…

  18. Recognition Tunneling

    OpenAIRE

    Lindsay, Stuart; He, Jin; Sankey, Otto; Hapala, Prokop; Jelinek, Pavel; Zhang, Peiming; Chang, Shuai; Huang, Shuo

    2010-01-01

    Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode (“tethered molecule-pair” configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel ...

  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. Direct Observation of Second Order Atom Tunnelling

    CERN Document Server

    Foelling, S; Cheinet, P; Feld, M; Saers, R; Widera, A; Müller, T; Bloch, I

    2008-01-01

    Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing novel dynamical behaviour can arise where particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade. Here we report on the first direct and time-resolved observation of correlated tunnelling of two interacting atoms through a barrier in a double well potential. We show that for weak interactions between the atoms and dominating tunnel coupling, individual atoms can tunnel independently, similar to the case in a normal Josephson junction. With strong repulsive interactions present, two atoms located on one side of the barrier cannot separate, but are observed to tunnel together as a pair in a second ...

  1. "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…

  2. Effect of interlayer tunneling on the electronic structure of bilayer cuprates and quantum phase transitions in carrier concentration and high magnetic field

    International Nuclear Information System (INIS)

    We present a theoretical study of the electronic structure of bilayer HTSC cuprates and its evolution under doping and in a high magnetic field. Analysis is based on the t-t?-t?-J* model in the generalized Hartree-Fock approximation. Possibility of tunneling between CuO2 layers is taken into account in the form of a nonzero integral of hopping between the orbitals of adjacent planes and is included in the scheme of the cluster form of perturbation theory. The main effect of the coupling between two CuO2 layers in a unit cell is the bilayer splitting manifested in the presence of antibonding and bonding bands formed by a combination of identical bands of the layers themselves. A change in the doping level induces reconstruction of the band structure and the Fermi surface, which gives rise to a number of quantum phase transitions. A high external magnetic field leads to a fundamentally different form of electronic structure. Quantum phase transitions in the field are observed not only under doping, but also upon a variation of the field magnitude. Because of tunneling between the layers, quantum transitions are also split; as a result, a more complex sequence of the Lifshitz transitions than in single-layer structures is observed.

  3. 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.

  4. 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

  5. Tunneling between Two Quantum Hall Droplets

    OpenAIRE

    Yang, Inseok; Kang, Woowon; Pfeiffer, Loren; Baldwin, Kirk; West, Ken

    2004-01-01

    We report on tunneling experiment between two quantum Hall droplets separated by a nearly ideal tunnel barrier. The device is produced by cleaved edge overgrowth that laterally juxtaposes two two-dimensional electron systems across a high quality semiconductor barrier. The dramatic evolution of the tunneling characteristics is consistent with the magnetic field-dependent tunneling between the coupled edge states of the quantum Hall droplets. We identify a series of quantum c...

  6. The LEP tunnel

    CERN Document Server

    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.

  7. Fowler-Nordheim electron tunneling mechanism in Ni/SiO2/n-4H SiC MOS devices

    Science.gov (United States)

    Kodigala, Subba Ramaiah; Chattopadhyay, S.; Overton, C.; Ardoin, I.

    2015-12-01

    The Ni/SiO2/n-type 4H SiC MOS devices have been fabricated for microelectronic device applications. The SiO2 layer employed in the MOS devices is grown by wet thermal oxidation process. The current-field characteristics of Ni/SiO2/n-type 4H SiC MOS devices are quiet interestingly studied by employing Fowler Nordheim (FN) conduction tunneling model, which is verified by theoretical simulation. It is learnt that the tunneling current through the barrier in the MOS devices promptly obeys the FN conduction tunneling mechanism. The simulation results show that the current in the MOS device increases and barrier height decreases with increasing temperature and internal electric field. Therefore, the correction factor for the barrier height of n-type 4H SiC/SiO2 MOS device due to the influence of both the temperature and internal electric field is employed. The barrier height observed by the experiments is apparently smaller than the simulated one of an ideal MOS device. However, after employing all the correction factors to the barrier height, the simulated current-field curves fairly coincide with the experimental results. The reason for obtaining smaller experimental barrier height for MOS devices is substantially explored with the support of current-field (J-F) analysis. On the other hand, this article comprehensively addresses the effects of quantum mechanical, interface trap density and thickness of 4H-SiC on the barrier height.

  8. Electronic textbooks as a professional resource after dental school.

    Science.gov (United States)

    Bates, Michael L; Strother, Elizabeth A; Brunet, Darlene P; Gallo, John R

    2012-05-01

    In two previous studies of dental students' attitudes about the VitalSource Bookshelf, a digital library of dental textbooks, students expressed negative opinions about owning and reading electronic textbooks. With the assumption that dentists would find the digital textbooks useful for patient care, the authors surveyed recent graduates to determine if their attitude toward the VitalSource Bookshelf had changed. A brief survey was sent to 119 alumni from the classes of 2009 and 2010 of one U.S. dental school. Forty-seven (39.5 percent) completed the questionnaire. Eighteen respondents (48.3 percent) reported using the e-textbooks often or sometimes. The twenty-nine dentists who said they have not used the collection since graduation reported preferring print books or other online sources or having technical problems when downloading the books to a new computer. Only five respondents selected the VitalSource Bookshelf as a preferred source of professional information. Most of the respondents reported preferring to consult colleagues (37.8 percent), the Internet (20 percent), or hardcopy books (17.8 percent) for information. When asked in an open-ended question to state their opinion of the Bookshelf, nineteen (42.2 percent) responded positively, but almost one-third of these only liked the search feature. Six respondents reported that they never use the program. Twenty-two said they have had technical problems with the Bookshelf, including fifteen who have not been able to install it on a new computer. Many of them said they have not followed up with either the dental school or VitalSource support services to overcome this problem. Our study suggests that dentists, similar to dental students, dislike reading electronic textbooks, even with the advantage of searching a topic across more than sixty dental titles. PMID:22550109

  9. 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...

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

    OpenAIRE

    Mallinath Kumbar; G. Kiran kumar

    2012-01-01

    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 ...

  11. Where Do Electronic Books Fit in the College Research Arsenal of Resources?

    Science.gov (United States)

    Barbier, Patricia

    2007-01-01

    Student use of electronic books has become an accepted supplement to traditional resources. Student use and satisfaction was monitored through an online course discussion board. Increased use of electronic books indicate this service is an accepted supplement to the print book collection.

  12. Electronic Information Resources in Undergraduate Education: An Exploratory Study of Opportunities for Student Learning and Independence.

    Science.gov (United States)

    McDowell, Liz

    2002-01-01

    This qualitative interview-based study examines lecturer perspectives on the roles of electronic information resources in undergraduate education. Highlights include electronic academic libraries; changes toward more constructivist approaches to learning; information quality on the Web; plagiarism; information use; information literacy; and…

  13. Using the Internet Gopher Protocol to link a computerized patient record and distributed electronic resources.

    OpenAIRE

    Hales, J. W.; Low, R. C.; Fitzpatrick, K T

    1993-01-01

    At Duke University Medical Center, we are developing a prototype clinical application for automated patient care plans with integrated links to electronic documents and other electronic resources. These links are implemented using the Internet Gopher Protocol, an emerging standard for distributed document search and retrieval. Use of this protocol permits storage of electronic documents in an open, nonproprietary manner. This paper discusses the architecture of the link mechanism and presents...

  14. 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

  15. ?????????????????????? 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.

  16. 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.

  17. 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

  18. Resonant structures in the low-energy electron continuum for single ionization of atoms in the tunnelling regime

    International Nuclear Information System (INIS)

    We present high-resolution fully differential experimental data on single ionization of He, Ne and Ar by ultra-short (25 fs, 6 fs) 795 nm laser pulses at intensities 0.15-2.0 x 1015 W cm-2. We show that the ATI-like pattern can survive deep in the tunnelling regime and that the atomic structure plays an important role in the formation of the low-energy photoelectron spectra even at high intensities. The absence of ponderomotive shifts, the splitting of the peaks and their degeneration for few-cycle pulses indicate that the observed structures originate from a resonant process. (letter to the editor)

  19. Electronic Structure on (001) Surface of BaFe2As2 Parent Compound Studied with Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Jayasundara, D. R.; Li, A.; Xuan, Y.; O'Neal, J. P.; Pan, S. H.; Jin, R.; Plummer, E. W.; Jin, R.; Sefat, A. S.; McGuire, M. A.; Sales, B. C.; Mandrus, D.

    2009-03-01

    Doping can drive some metallic pnictide compounds to superconducting phase. The microscopic mechanism of this phase transition has still not been understood. Starting with the parent compound, we have used a UHV Low Temperature STM to study the density of states on the (001) surface of single crystal BaFe2As2. The tunneling spectrum varies depending on the local environment. All the spectrums have the same background with density of states depression near the Fermi energy, but some of them show different anomalies. We attribute some of these anomalies to surface states. These results may provide useful information to those surface techniques other than STM.

  20. Low-dimensional NbO structures on the Nb(110) surface: scanning tunneling microscopy, electron spectroscopy and diffraction

    OpenAIRE

    Razinkin, A. S.; Shalaeva, E. V.; Kuznetsov, M. V.

    2008-01-01

    X-ray photoelectron spectroscopy and diffraction (XPS, XPD) and scanning tunneling microscopy (STM) have been used for study of NbOx-structures on the Nb(110) surface. It is shown that niobium atoms are ordered to form a two-dimensional superstructure with equidistant spacing between the chains of niobium atoms. Chemical shifts of Nb3d- and O1s-levels demonstrate that the oxide layer corresponds to niobium monoxide NbO and the most part of oxygen in chemisorbed state is loca...

  1. 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.)

  2. Insights into electron tunneling across hydrogen-bonded base-pairs in complete molecular circuits for single-stranded DNA sequencing

    International Nuclear Information System (INIS)

    We report a first-principles study of electron ballistic transport through a molecular junction containing deoxycytidine-monophosphate (dCMP) connected to metal electrodes. A guanidinium ion and guanine nucleobase are tethered to gold electrodes on opposite sides to form hydrogen bonds with the dCMP molecule providing an electric circuit. The circuit mimics a component of a potential device for sequencing unmodified single-stranded DNA. The molecular conductance is obtained from DFT Green's function scattering methods and is compared to estimates from the electron tunneling decay constant obtained from the complex band structure. The result is that a complete molecular dCMP circuit of 'linker((CH2)2)-guanidinium-phosphate-deoxyribose-cytosine-guanine' has a very low conductance (of the order of fS) while the hydrogen-bonded guanine-cytosine base-pair has a moderate conductance (of the order of tens to hundreds of nS). Thus, while the transverse electron transfer through base-pairing is moderately conductive, electron transfer through a complete molecular dCMP circuit is not. The gold Fermi level is found to be aligned very close to the HOMO for both the guanine-cytosine base-pair and the complete molecular dCMP circuit. Results for two different plausible geometries of the hydrogen-bonded dCMP molecule reveal that the conductance varies from fS for an extended structure to pS for a slightly compressed structure.

  3. Signatures of electron-magnon interaction in charge and spin current in magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach

    Science.gov (United States)

    Mahfouzi, Farzad; Nikolic, Branislav; QTTG Team

    2014-03-01

    We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the perturbation expansion for the electron and magnon self-energies of the nonequilibrium Green function (NEGF) formalism applied to electron-magnon (e-m) interacting system driven out of equilibrium by finite bias voltage. This is then employed to understand the effect of inelastic e-m scattering on current-voltage (I-V) characteristics of F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs). For this purpose, we evaluate self-consistently Fock diagram for the electron self-energy which ensures charge current conservation (i.e., sum of charge currents in all leads must be zero), as well as electron-hole polarization bubble diagram for magnon self-energy, where respective GF lines within these diagrams are the fully interacting ones. Furthermore we present the formulation to calculate the Fano factor in correlated systems out of equilibrium and then investigate the effect of e-m coupling on noise in MTJs. This work was supported in part by NSF under Grant No. ECCS 1202069.

  4. Insights into electron tunneling across hydrogen-bonded base-pairs in complete molecular circuits for single-stranded DNA sequencing

    Science.gov (United States)

    Lee, Myeong H.; Sankey, Otto F.

    2009-01-01

    We report a first-principles study of electron ballistic transport through a molecular junction containing deoxycytidine-monophosphate (dCMP) connected to metal electrodes. A guanidinium ion and guanine nucleobase are tethered to gold electrodes on opposite sides to form hydrogen bonds with the dCMP molecule providing an electric circuit. The circuit mimics a component of a potential device for sequencing unmodified single-stranded DNA. The molecular conductance is obtained from DFT Green's function scattering methods and is compared to estimates from the electron tunneling decay constant obtained from the complex band structure. The result is that a complete molecular dCMP circuit of 'linker((CH2)2)-guanidinium-phosphate-deoxyribose-cytosine-guanine' has a very low conductance (of the order of fS) while the hydrogen-bonded guanine-cytosine base-pair has a moderate conductance (of the order of tens to hundreds of nS). Thus, while the transverse electron transfer through base-pairing is moderately conductive, electron transfer through a complete molecular dCMP circuit is not. The gold Fermi level is found to be aligned very close to the HOMO for both the guanine-cytosine base-pair and the complete molecular dCMP circuit. Results for two different plausible geometries of the hydrogen-bonded dCMP molecule reveal that the conductance varies from fS for an extended structure to pS for a slightly compressed structure.

  5. 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…

  6. A Study on Developing Evaluation Criteria for Electronic Resources in Evaluation Indicators of Libraries

    Science.gov (United States)

    Noh, Younghee

    2010-01-01

    This study aimed to improve the current state of electronic resource evaluation in libraries. While the use of Web DB, e-book, e-journal, and other e-resources such as CD-ROM, DVD, and micro materials is increasing in libraries, their use is not comprehensively factored into the general evaluation of libraries and may diminish the reliability of…

  7. Universal tunneling time for all fields

    CERN Document Server

    Nimtz, G

    2007-01-01

    Tunneling is an important physical process. The observation that particles surmount a high mountain in spite of the fact that they don't have the necessary energy cannot be explained by classical physics. However, this so called tunneling became allowed by quantum mechanics. Experimental tunneling studies with different photonic barriers from microwave frequencies up to ultraviolet frequencies pointed towards a universal tunneling time (Haibel,Esposito). Experiments and calculations have shown that the tunneling time of opaque photonic barriers (optical mirrors, e.g.) equals approximately the reciprocal frequency of the corresponding electromagnetic wave. The tunneling process is described by virtual photons. Virtual particles like photons or electrons are not observable. However, from the theoretical point of view, they represent necessary intermediate states between observable real states. In the case of tunneling there is a virtual particle between the incident and the transmitted particle. Tunneling modes...

  8. Differences in Tunneling Time between 77 K and Room Temperature for Tunneling Biquantum Wells

    Science.gov (United States)

    Tackeuchi, Atsushi; Sugiyama, Yoshihiro; Inata, Tsuguo; Muto, Shunichi

    1992-12-01

    We measured the recovery time from excitonic absorption bleaching in tunneling biquantum wells at 77 K and room temperature. The absorption recovery time corresponds to the tunneling time of electrons from narrow to wide wells. We have found that tunneling at 77 K is about 2.5 times slower than at room temperature.

  9. Assessment of the utilisation of Makerere University electronic information resources by academic staff; challenges and prospects

    OpenAIRE

    Agaba, Didace Mulamira

    2005-01-01

    The study investigated the utilization of electronic information resources by the academic staff of Makerere University in Uganda. It examined academic staff awareness of the resources’ availability, the types of resources provided by the University Library , factors affecting their utilization, problems faced, and it offers recommendations for the way forward. The study was both qualitative and quantitative in nature, employing questionnaire, interview and content analysis methods. Findings ...

  10. 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...

  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. Electron tunneling current in isotropic n+Poly-Si/HfSiOxN/Trap/SiO2/p-Si capacitors: Effect of the depth and width traps and Si orientation

    Science.gov (United States)

    Noor, Fatimah A.; Khairiah, Abdullah, Mikrajuddin; Khairurrijal

    2013-09-01

    In this work, we studied electron transmittance and tunneling current in isotropic n+Poly-Si/HfSiOxN/Trap/SiO2/p-Si capacitors by including the coupling effect between transverse and longitudinal kinetic energies represented by an electron velocity in the gate. It was used an HfSiOxN/SiO2 dual ultrathin layer as the gate oxide in an isotropic n+poly-Si/oxide/Si capacitor to replace SiO2. The charge trapping formed at the HfSiOxN/SiO2 interface is the main problem in using HfSiOxN because it can affect the performance of the device. Additionally, the tunneling current in metal-oxide-semiconductor (MOS) capacitor with high-? dielectric stacks is almost zero at low bias voltage regime without considering the effect of trap. Hence, it is necessary to develop a model of tunneling current with considering the trap effect at the HfSiOxN/SiO2 interface. The transmittance was numerically calculated by employing a transfer matrix method. The transmittance was then applied to calculate tunneling currents in the structure. The effects of the depth and width traps, and the silicon substrate orientation on the transmittance and tunneling current are studied by utilizing the developed model.

  13. 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.

  14. Tunneling current induced phonon generation in nanostructures

    OpenAIRE

    Arseyev, P. I.; Maslova, N. S.

    2006-01-01

    We analyze generation of phonons in tunneling structures with two electron states coupled by electron-phonon interaction. The conditions of strong vibration excitations are determined and dependence of non-equilibrium phonon occupation numbers on the applied bias is found. For high vibration excitation levels self consistent theory for the tunneling transport is presented.

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

    Directory of Open Access Journals (Sweden)

    Aaron August Lupton

    2012-01-01

    Full Text Available 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, did just that by building a system called Managing University Library Electronic Resources (MULER. The article details the background and history of how electronic resources were managed pre-MULER; why a new ERM was needed; the planning process; the current and innovative functions of MULER, including integration of MULER data into York University Libraries search and discovery layer, Vufind; subject tagging in MULER; new functions to be added; and lessons learned from the project. Positive and negative implications of choosing an in-house project over paying for a commercial product are also discussed.

  16. Tunnel magnetoresistance in magnetic tunnel junctions with embedded nanoparticles

    CERN Document Server

    Useinov, Arthur; Ye, Lin-Xiu; Wu, Te-Ho; Lai, Chih-Huang

    2015-01-01

    In this paper, we attempt the theoretical modeling of the magnetic tunnel junctions with embedded magnetic and nonmagnetic nanoparticles (NPs). A few abnormal tunnel magnetoresistance (TMR) effects, observed in related experiments, can be easily simulated within our model: we found, that the suppressed TMR magnitudes and the TMR sign-reversing effect at small voltages are related to the electron momentum states of the NP located inside the insulating layer. All these TMR behaviors can be explained within the tunneling model, where NP is simulated as a quantum well (QW). The coherent (direct) double barrier tunneling is dominating over the single barrier one. The origin of the TMR suppression is the quantized angle transparency for spin polarized electrons being in one of the lowest QW states. The phenomenon was classified as the quantized conductance regime due to restricted geometry.

  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. Conducting ballistic magnetoresistance and tunneling magnetoresistance: Pinholes and tunnel barriers

    OpenAIRE

    García García, Nicolás

    2000-01-01

    This letter shows that conducting ballistic and tunneling magnetoresistances have identical physical treatments and, therefore, it is not possible to distinguish whether an experiment is measuring, in oxide barriers, electron conduction through pinholes or tunneling because both types of conduction are governed by the same physics. Currents in both cases are calculated by matching wave functions at the electrodes (both are ballistic). Therefore, pinholes or small ballistic nanocontacts in the...

  19. Tunneling spectroscopy studies of aluminum oxide tunnel barrier layers

    CERN Document Server

    Mather, P G; Tan, E; Read, J C; Buhrman, R A

    2005-01-01

    We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. The former, if sufficiently energetic, results in locally well defined conduction band onsets at ~1 V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 C thermal anneals.

  20. Eavesdropping on Electronic Guidebooks Observing Learning Resources in Shared Listening Environments

    CERN Document Server

    Woodruff, A; Grinter, R E; Hurst, A; Szymanski, M H; Thornton, J D; Woodruff, Allison; Aoki, Paul M.; Grinter, Rebecca E.; Hurst, Amy; Szymanski, Margaret H.; Thornton, James D.

    2002-01-01

    We describe an electronic guidebook, Sotto Voce, that enables visitors to share audio information by eavesdropping on each other's guidebook activity. We have conducted three studies of visitors using electronic guidebooks in a historic house: one study with open air audio played through speakers and two studies with eavesdropped audio. An analysis of visitor interaction in these studies suggests that eavesdropped audio provides more social and interactive learning resources than open air audio played through speakers.

  1. Eavesdropping on Electronic Guidebooks: Observing Learning Resources in Shared Listening Environments

    OpenAIRE

    Woodruff, Allison; Aoki, Paul M.; Grinter, Rebecca E.; Hurst, Amy; Szymanski, Margaret H.; Thornton, James D.

    2002-01-01

    We describe an electronic guidebook, Sotto Voce, that enables visitors to share audio information by eavesdropping on each other's guidebook activity. We have conducted three studies of visitors using electronic guidebooks in a historic house: one study with open air audio played through speakers and two studies with eavesdropped audio. An analysis of visitor interaction in these studies suggests that eavesdropped audio provides more social and interactive learning resources...

  2. 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.

  3. 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.

  4. Library Electronic Resource Sharing Among Liberal Arts Colleges: ACS Palladian Alliance Project

    Directory of Open Access Journals (Sweden)

    Wenxian Zhang

    1997-03-01

    Full Text Available ?Effective electronic resource sharing is critical to library information services of the 1990s. Explosion of data and increased cost of information force libraries to work together, and technological advancements present the library service profession a platform for resource sharing. The Palladian Alliance Project of the Associated Colleges of the South is designed to provides ACS member institutions an effective means to enhance information access for their faculty and students, and achieve significant cost containment in the years to come.

  5. Evaluating a scalable model for implementing electronic health records in resource-limited settings

    OpenAIRE

    Were, Martin C.; Emenyonu, Nneka; Achieng, Marion; Shen, Changyu; Ssali, John; Masaba, John P M; William M. Tierney

    2010-01-01

    Current models for implementing electronic health records (EHRs) in resource-limited settings may not be scalable because they fail to address human-resource and cost constraints. This paper describes an implementation model which relies on shared responsibility between local sites and an external three-pronged support infrastructure consisting of: (1) a national technical expertise center, (2) an implementer's community, and (3) a developer's community. This model was used to implement an op...

  6. Insights into electron tunneling across hydrogen-bonded base-pairs in complete molecular circuits for single-stranded DNA sequencing

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Myeong H; Sankey, Otto F [Department of Physics, Arizona State University, Tempe, AZ 85287-1504 (United States)

    2009-01-21

    We report a first-principles study of electron ballistic transport through a molecular junction containing deoxycytidine-monophosphate (dCMP) connected to metal electrodes. A guanidinium ion and guanine nucleobase are tethered to gold electrodes on opposite sides to form hydrogen bonds with the dCMP molecule providing an electric circuit. The circuit mimics a component of a potential device for sequencing unmodified single-stranded DNA. The molecular conductance is obtained from DFT Green's function scattering methods and is compared to estimates from the electron tunneling decay constant obtained from the complex band structure. The result is that a complete molecular dCMP circuit of 'linker((CH{sub 2}){sub 2})-guanidinium-phosphate-deoxyribose-cytosine-guanine' has a very low conductance (of the order of fS) while the hydrogen-bonded guanine-cytosine base-pair has a moderate conductance (of the order of tens to hundreds of nS). Thus, while the transverse electron transfer through base-pairing is moderately conductive, electron transfer through a complete molecular dCMP circuit is not. The gold Fermi level is found to be aligned very close to the HOMO for both the guanine-cytosine base-pair and the complete molecular dCMP circuit. Results for two different plausible geometries of the hydrogen-bonded dCMP molecule reveal that the conductance varies from fS for an extended structure to pS for a slightly compressed structure.

  7. Superluminal Tunneling Devices

    OpenAIRE

    Nimtz, Günter

    2002-01-01

    Photonic tunneling permits superluminal signal transmission. The principle of causality is not violated but the time duration between cause and effect can be shortened compared with an interaction exchange with velocity of light. This outstanding property can be applied to speed-up photonic signal modulation and transmission as well as to improve micro-electronic devices. Superluminal photonic signal transmission have been presented at microwave and infrared frequencies alre...

  8. 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

  9. Magneto-transport characteristics of electron-doped Ca0.85Sm0.15MnO3 manganite: Hopping and tunneling

    Science.gov (United States)

    Hossain Khan, Momin; Pal, Sudipta

    2015-11-01

    In this work we have reported the temperature and magnetic field dependence of resistivity and magnetoresistance in electron-doped polycrystalline Ca0.85Sm0.15MnO3 (CSMO). It shows a robust semiconducting behavior down to the lowest temperature (5 K) of investigation. High-T resistivity of the present sample follows small polaron hopping (SPH) conduction mechanism. The variable range hopping (VRH) model has been found to fit low-T resistivity data. Intermediate-temperature ?(T) data has been explained using a parallel combination of SPH and 3D-VRH model. The resistivity shows strong dependence on the magnetic field-temperature history. Magnetoresistance (MR) of the sample shows strong irreversibility with respect to sweeping of the field between the highest positive and negative values. Low-? state of the envelope curve in MR indicates a manifestation of kinetic arrest of the electronic phase on application of magnetic field. We demonstrates that the sizable MR at low fields dominated by spin-polarized tunneling between the adjacent grains.

  10. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.; Sadowski, J.; Guertler, C.M.; Bland, J.A.C.; Rasmussen, Finn Berg

    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.

  11. We're All in This Together: Library Faculty and Staff and Their Reporting of Electronic Resource Problems

    Science.gov (United States)

    Foster, Anita; Williams, Sarah C.

    2010-01-01

    Libraries continue to shift budgets toward obtaining more electronic resources. Electronic resources can develop problems at any time when a library offers access. Staff collaboration is vital in ensuring availability to those resources. Partnering with areas in the library that work most closely with patrons can help share the load of the…

  12. Connecting knowledge resources to the veterinary electronic health record: opportunities for learning at point of care.

    Science.gov (United States)

    Alpi, Kristine M; Burnett, Heidi A; Bryant, Sheila J; Anderson, Katherine M

    2011-01-01

    Electronic health records (EHRs) provide clinical learning opportunities through quick and contextual linkage of patient signalment, symptom, and diagnosis data with knowledge resources covering tests, drugs, conditions, procedures, and client instructions. This paper introduces the EHR standards for linkage and the partners-practitioners, content publishers, and software developers-necessary to leverage this possibility in veterinary medicine. The efforts of the American Animal Hospital Association (AAHA) Electronic Health Records Task Force to partner with veterinary practice management systems to improve the use of controlled vocabulary is a first step in the development of standards for sharing knowledge at the point of care. The Veterinary Medical Libraries Section (VMLS) of the Medical Library Association's Task Force on Connecting the Veterinary Health Record to Information Resources compiled a list of resources of potential use at point of care. Resource details were drawn from product Web sites and organized by a metric used to evaluate medical point-of-care resources. Additional information was gathered from questions sent by e-mail and follow-up interviews with two practitioners, a hospital network, two software developers, and three publishers. Veterinarians with electronic records use a variety of information resources that are not linked to their software. Systems lack the infrastructure to use the Infobutton standard that has been gaining popularity in human EHRs. While some veterinary knowledge resources are digital, publisher sites and responses do not indicate a Web-based linkage of veterinary resources with EHRs. In order to facilitate lifelong learning and evidence-based practice, veterinarians and educators of future practitioners must demonstrate to veterinary practice software developers and publishers a clinically-based need to connect knowledge resources to veterinary EHRs. PMID:22023919

  13. 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…

  14. Implementation of an Electronic Resource Assessment System in an Academic Library

    Science.gov (United States)

    Xu, Fei

    2010-01-01

    Purpose: The purpose of this paper is to provide a library with useful information about selection criteria for an electronic resource assessment system and practical assistance on how to implement efficiently such a system. Design/methodology/approach: The paper is based on literature review, desk research, and implementation experience.…

  15. What Do Community College Libraries Do with Electronic Resources? The Practice in 2003

    Science.gov (United States)

    Shorten, Jay

    2004-01-01

    One hundred fourteen community college libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, ready reference, and their own catalogue both on their home page and within their web site. They do not usually…

  16. A Survey of the Use of Electronic Resources at Seven Universities in Wuhan, China

    Science.gov (United States)

    Zhang, Liyi; Ye, Pinghao; Liu, Qihua

    2011-01-01

    Purpose: The purpose of this paper is to report on users' information behaviour in China, a topic which has not been researched extensively. The aim is to help producers and providers collect and develop more electronic resources. Design/methodology/approach: The study investigates users' information behaviour at seven "211 Project" universities…

  17. Innovative's Electronic Resource Management as catalyst for change at Glasgow University Library

    OpenAIRE

    Galloway, L

    2006-01-01

    In March 2003 Glasgow University Library joined with Innovative and several other Innovative customers to develop a new Electronic Resource Management (ERM) module. This paper will outline the ways in which the development and implementation of ERM has acted as a catalyst and facilitator for further enhancements and developments in the area of e-journals at Glasgow University Library.

  18. Effect of electron trap states on spin-dependent transport characteristics in CoFe/MgO/n+-Si junctions investigated by Hanle effect measurements and inelastic electron tunneling spectroscopy

    International Nuclear Information System (INIS)

    Spin-dependent transport properties in CoFe/MgO/n+-Si junctions were investigated by Hanle effect measurements and inelastic electron tunneling (IET) spectroscopy. The CoFe/MgO/n+-Si junctions examined in this study exhibited two different Hanle curves. In the low bias region, broad Hanle signals were mainly observed; in the high bias region, narrow Hanle signals were mainly observed. The d2I/dV2-V curves (which correspond to IET spectra) contain several peaks originating from phonon modes and other peaks originating from electron trap states. At the bias voltage where electron trap states are observed, ?d2I/dV2 depends on the magnetic field and the full width at half-maximum of the ?d2I/dV2–H curves corresponds to that of the broad Hanle signals. These results indicate that electron trap states are located in the low energy region and cause a decrease in spin lifetime

  19. Effect of electron trap states on spin-dependent transport characteristics in CoFe/MgO/n{sup +}-Si junctions investigated by Hanle effect measurements and inelastic electron tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Inokuchi, Tomoaki, E-mail: tomoaki.inokuchi@toshiba.co.jp; Ishikawa, Mizue; Sugiyama, Hideyuki; Tanamoto, Tetsufumi; Saito, Yoshiaki [Toshiba Corporation Corporate R and D Center, Toshiba Corporation, Kawasaki 212-8582 (Japan)

    2014-12-08

    Spin-dependent transport properties in CoFe/MgO/n{sup +}-Si junctions were investigated by Hanle effect measurements and inelastic electron tunneling (IET) spectroscopy. The CoFe/MgO/n{sup +}-Si junctions examined in this study exhibited two different Hanle curves. In the low bias region, broad Hanle signals were mainly observed; in the high bias region, narrow Hanle signals were mainly observed. The d{sup 2}I/dV{sup 2}-V curves (which correspond to IET spectra) contain several peaks originating from phonon modes and other peaks originating from electron trap states. At the bias voltage where electron trap states are observed, ?d{sup 2}I/dV{sup 2} depends on the magnetic field and the full width at half-maximum of the ?d{sup 2}I/dV{sup 2}–H curves corresponds to that of the broad Hanle signals. These results indicate that electron trap states are located in the low energy region and cause a decrease in spin lifetime.

  20. Considering Point-of-Care Electronic Medical Resources in Lieu of Traditional Textbooks for Medical Education.

    Science.gov (United States)

    Hale, LaDonna S; Wallace, Michelle M; Adams, Courtney R; Kaufman, Michelle L; Snyder, Courtney L

    2015-09-01

    Selecting resources to support didactic courses is a critical decision, and the advantages and disadvantages must be carefully considered. During clinical rotations, students not only need to possess strong background knowledge but also are expected to be proficient with the same evidence-based POC resources used by clinicians. Students place high value on “real world” learning and therefore may place more value on POC resources that they know practicing clinicians use as compared with medical textbooks. The condensed nature of PA education requires students to develop background knowledge and information literacy skills over a short period. One way to build that knowledge and those skills simultaneously is to use POC resources in lieu of traditional medical textbooks during didactic training. Electronic POC resources offer several advantages over traditional textbooks and should be considered as viable options in PA education. PMID:26309211

  1. 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....

  2. 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

  3. Resonant photon-assisted tunneling through a double quantum dot an electron pump from spatial Rabi oscillations

    CERN Document Server

    Stafford, C A; Stafford, Charles A; Wingreen, Ned S

    1996-01-01

    The time average of the fully nonlinear current through a double quantum dot, subject to an arbitrary combination of ac and dc voltages is calculated exactly using the Keldysh nonequilibrium Green function technique. When driven on resonance, the system functions as an efficient electron pump due to Rabi oscillation between the dots. The pumping current is maximum when the coupling to the leads equals the Rabi frequency.

  4. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    McEwen, Gerald D.; Chen Fan [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States); Zhou Anhong, E-mail: Anhong.Zhou@usu.edu [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States)

    2009-06-08

    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 (D{sub 0}), surface coverage ({theta}{sub R}), and monolayer thickness (d{sub i}) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density ({Gamma}{sub 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: {Gamma}{sub DNA} (dsS-DNA/Au) > {Gamma}{sub DNA} (MCH/dsS-DNA/Au) > {Gamma}{sub 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/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.

  5. 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/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.

  6. Chiral tunneling in trilayer graphene

    OpenAIRE

    kumar, S. Bala; Guoa, Jing

    2012-01-01

    We study the effect of chiral-tunneling in Bernal and Rombhohedral stacked trilayer-graphene (3LG). Based on the chirality of the electronic bands, at the K-point, (Rombhohedral) Bernal-3LG exhibits 100% (50%) transparency across a heterojunction. Utilizing this property, we further investigate the effect of electron collimation in 3LG. Due to the difference in the Berry's phase, we show that, Rombhohedral-3LG is a better electron collimator, compared to monolayer and Bernal...

  7. 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.

  8. 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.

  9. The Impact of Electronic Banking on Human Resources Performance in the Nigerian Banking Industry

    OpenAIRE

    Ojokuku, R. M.; Sajuyigbe, A. S.

    2012-01-01

    The survey examined the impact of electronic banking on Human Resource (HR) performance in the Nigerian banking industry, using First Bank Plc as a case study. The objective was to determine how the introduction of e-Banking has impacted on the efficiency and effectiveness of service delivery by the bank's personnel and on bank-customers relationship and customer satisfaction. Structured questionnaire was used with the aid of personal interview to collect data from thirty five respondents ran...

  10. Demographic Variables of University Teachers and Usage of Electronic Information Resources: A Case in Sri Lanka

    OpenAIRE

    Nadarajah Sivathaasan; Sivapalan Achchuthan; Rajendran Kajananthan

    2013-01-01

    The primary aim of the study is to identify whether there are any significant mean differences amongdemographic variables such as gender, age group, faculty, teaching language and experience of universityteachers employed at the University of Jaffna, Sri Lanka on the usage of electronic information resources (EIR).The study employs independent samples t- test and one-way ANOVA (f-test) to test the operational hypotheses.The survey method used in this study is a questionnaire and a total of 7...

  11. Bit by Bit: A Series of Trends, Tools, and Initiatives Are Aimed at Improving Electronic Resource Management

    Science.gov (United States)

    Webster, Peter

    2006-01-01

    Electronic resources are more prominent than ever in library collections, yet they resist easy management. A range of tools and cooperative efforts are emerging to improve the management and evaluation of electronic resources. Initiatives are underway to standardize and automate the harvesting of usage statistics and e-journal title and holdings…

  12. Knowledge and use of electronic information resources by medical sciences faculty at The University of the West Indies

    OpenAIRE

    Renwick, Shamin

    2005-01-01

    Objective: The objective was to determine faculty's knowledge of electronic resources, access to a computer, use of electronic resources (both number and frequency) available at the Medical Sciences Library (MSL), and the areas of training needed and to identify areas for further research.

  13. QUANTUM TUNNELLING AND MAGNETIZATION DYNAMICS IN LOW DIMENSIONAL SYSTEMS

    Directory of Open Access Journals (Sweden)

    ANDREA CORNIA

    2011-12-01

    Full Text Available Quantum mechanics allows a system to overcome a classically-unsurmountable energy barrier through a mechanism called Quantum Tunnelling (QT. Although pertaining to the quantum domain, QT is the cause of important physical phenomena that can be detected at the macroscopic scale. Some of them have led to breakthrough applications in electronics (tunnel junctions and imaging (scanning tunnelling microscope.

  14. 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…

  15. Investigation into scanning tunnelling luminescence microscopy

    CERN Document Server

    Manson-Smith, S K

    2001-01-01

    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 provi...

  16. 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.

  17. Carpal Tunnel Surgery

    Medline Plus

    Full Text Available ... carried out for the condition of carpal tunnel syndrome. Carpal Tunnel Syndrome is a neuropathy where the median nerve gets ... of the hand. The surgery for carpal tunnel syndrome consists of a release of the transverse carpal ...

  18. 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.

  19. Endoscopic versus open carpal tunnel release for idiopathic carpal tunnel syndrome: a meta-analysis of randomized controlled trials

    OpenAIRE

    Zuo, Dongqing; ZHOU, ZIFEI; WANG, HONGSHENG; Liao, Yuxin; Zheng, Longpo; HUA, YINGQI; Cai, Zhengdong

    2015-01-01

    The objective of this study is to do a meta-analysis of the literature and compare the safety and efficacy of endoscopic carpal tunnel release (ECTR) and open carpal tunnel release (OCTR) for idiopathic carpal tunnel syndrome (CTS). A comprehensive literature search of the electronic databases MEDLINE, EMBASE, Google Scholar, and the Cochrane Controlled Trial Register was undertaken for randomized studies reporting carpal tunnel syndrome treated with ECTR or OCTR. The quality of randomized tr...

  20. 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.

  1. 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.)

  2. Laser tunneling from aligned molecules

    CERN Document Server

    Smeenk, C T L; Sokolov, A V; Spanner, M; Lee, K F; Staudte, A; Villeneuve, D M; Corkum, P B

    2013-01-01

    We study multi-photon ionization from N_2, O_2 and benzene using circularly polarized light. By examining molecular frame photo-electron angular distributions, we illustrate how multi-photon ionization acts a momentum-selective probe of the local electron density in the Dyson orbitals for these molecules. We find good agreement with calculations based on a tunneling model and including saturation effects.

  3. Inelastic scattering in resonant tunneling

    OpenAIRE

    Wingreen, Ned S.; Jacobsen, Karsten Wedel; Wilkins, John W.

    1989-01-01

    The exact resonant-tunneling transmission probability for an electron interacting with phonons is presented in the limit that the elastic coupling to the leads is independent of energy. The phonons produce transmission sidebands but do not affect the integrated transmission probability or the escape rate of the electron from the resonant site. In the Appendixes, we evaluate the Green function that appears in the expression for the transmission probability.

  4. An electronic resource to support staff providing end of life care.

    Science.gov (United States)

    Pordes, Philippa; Ashcroft, Angela; Williams, Pauline

    The Department of Health's End of Life Care Strategy provided the opportunity to develop effective care, regardless of the setting. However, providing end of life care is challenging for all healthcare practitioners, with each care setting experiencing unique challenges. Within one acute NHS trust, the challenges of identifying and diagnosing dying were identified. An electronic resource tool was developed to aid prognostication and provide a single point of reference to assist healthcare practitioners in improving end of life care for patients in an acute hospital setting. PMID:22216666

  5. A survey of the use of electronic scientific information resources among medical and dental students

    OpenAIRE

    Aarnio Matti; Romanov Kalle

    2006-01-01

    Abstract Background To evaluate medical and dental students' utilization of electronic information resources. Methods A web survey sent to 837 students (49.9% responded). Results Twenty-four per cent of medical students and ninteen per cent of dental students searched MEDLINE 2+ times/month for study purposes, and thiry-two per cent and twenty-four per cent respectively for research. Full-text articles were used 2+ times/month by thirty-three per cent of medical and ten per cent of dental stu...

  6. 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.

  7. 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.

  8. Design of accelerator tunnel

    International Nuclear Information System (INIS)

    There are several key points in designing the underground tunnel where a large-sized accelerator is installed in. The following two points are very important. (1) A transformation of the tunnel is smaller. (2) Integrity and durability of the tunnel structure is higher. In order to accomplish a smaller transformation of the tunnel and a stable operation of the accelerator, we recommend not to provide the expansion joints to the tunnel. We performed the structural analysis on temperature change inside the tunnel without expansion joints. As a result, no problem was confirmed about crack and transformation of the tunnel. (author)

  9. Librarians' perceptions on the use of electronic resources at Catalan academic libraries: results of a focus group

    OpenAIRE

    Ollé, Candela; Borrego, Àngel

    2010-01-01

    The aim of this paper is to expand on previous quantitative and qualitative research into the use of electronic information resources and its impact on the information behaviour of academics at Catalan universities.

  10. 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 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.

  11. Superpoissonian shot noise in organic magnetic tunnel junctions

    OpenAIRE

    Cascales, Juan Pedro; Hong, Jhen-Yong; Martinez, Isidoro; Lin, Minn-Tsong; Szczepanski, Tomasz; Dugaev, Vitalii K.; Barnas, Jozef; Aliev, Farkad G.

    2015-01-01

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here we investigate conductance and shot noise in magnetic tunnel junctions with PTCDA barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10 and 40\\%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5-2 times...

  12. Inherent thermometry in a hybrid superconducting tunnel junction

    OpenAIRE

    Courtois, Hervé; Rajauria, Sukumar; Gandit, Philippe; Hekking, Frank; Pannetier, Bernard

    2008-01-01

    We discuss inherent thermometry in a Superconductor - Normal metal - Superconductor tunnel junction. In this configuration, the energy selectivity of single-particle tunneling can provide a significant electron cooling, depending on the bias voltage. The usual approach for measuring the electron temperature consists in using an additional pair of superconducting tunnel junctions as probes. In this paper, we discuss our experiment performed on a different design with no such ...

  13. 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.

  14. Assessment of accepting rate of Electronic Information Resources (EIR by Iranian Knowledge and Information Science faculty members

    Directory of Open Access Journals (Sweden)

    Afshin Hamdipour

    2014-12-01

    Full Text Available Electronic information resources (EIR play an important role in the process of education and research. The aim of this study was to analyze the status of adoption of electronic information resources (EIR by Iranian Knowledge and Information Science (KIS faculty members. This applied- descriptive survey was carried out on Iranian KIS Faculty Members in 2012. The number of participants was determined based on the Cochran's sample size table. Of the 170 Faculty Members, 122 individuals were randomly selected. Data collection tool was an Electronic questionnaire, and its validity was confirmed by professionals. The reliability of the questionnaire was verified after a pilot study. By using IBM SPSS 20 software and through exploratory factor analysis, descriptive statistics, and inferential tests the data were analyzed. Results showed that, there is significant difference between the mean of adoption rate of electronic information resources (EIR by people with different levels of education. In addition, the Pearson correlation coefficient showed a significant relationship between mean of adoption rate and the faculty’s teaching experience and age. The results of Kolmogorov-Smirnoff test showed that the curve of adoption rate of electronic information resources among the sample is normal, and thus, the adoption rate of resources over time, is S-shaped. Ultimately, this study confirmed The Rogers’ Diffusion of Innovation Theory (2003 in context of Adaptor categories of electronic information resources (EIR, and S-shaped curve, among faculty members in departments of knowledge and Information science in Iran.

  15. Drill and blast tunnelling; Konvensjonell drift av tunneler

    Energy Technology Data Exchange (ETDEWEB)

    Roenn, Paal-Egil

    1997-12-31

    This thesis treats drill and blast tunnelling. The rapid technological advance necessitates revised and updated design criteria, quality requirements and quality control. In situ blast experiments were carried out in order to test new methods and improve the basis for calculation and design. The main topics of the experiments were (1) longer rounds and increased drillhole diameter, (2) emulsion slurry as explosives in tunnelling, and (3) electronic detonators in contour blasting. The experiments show that it is technically feasible to blast rounds of up to 8.6 m length. Using current technology, the economical optimum round length is substantially shorter. Dust, low visibility, noise and toxic fumes are occupational environmental strains for the tunnel workers. Several of the environmental factors are strongly influenced by the type of explosives used. For example, emulsion slurry resulted in 4 to 5 times better visibility than Anolit and the concentration of respirable dust and total dust was reduced by 30-50 %. Electronic detonators were tested and found to give a higher percentage of remaining drillholes in the contour than Nonel detonators. The thesis includes a chapter on economic design of hydropower tunnels. 42 refs., 83 figs., 45 tabs.

  16. Interface effects in spin-dependent tunneling

    CERN Document Server

    Tsymbal, E Y; Velev, J P; Jaswal, S S; Van Schilfgaarde, M; Oleynik, I I; Stewart, D A

    2005-01-01

    In the past few years the phenomenon of spin dependent tunneling (SDT) in magnetic tunnel junctions (MTJs) has aroused enormous interest and has developed into a vigorous field of research. The large tunneling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible application in random access memories and magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. One such question is the role of interfaces in MTJs and their effect on the spin polarization of the tunneling current and TMR. In this paper we consider different models which suggest that the spin polarization is primarily determined by the electronic and atomic structure of the ferromagnet/insulator interfaces rather than by their bulk properties. First, we consider a simple tight-binding model which demonstrates that the existence of interface states and their contribution to the tunneling current depend on the degree of hybridization between the orbitals on metal and insulator...

  17. Impact of Knowledge Resources Linked to an Electronic Health Record on Frequency of Unnecessary Tests and Treatments

    Science.gov (United States)

    Goodman, Kenneth; Grad, Roland; Pluye, Pierre; Nowacki, Amy; Hickner, John

    2012-01-01

    Introduction: Electronic knowledge resources have the potential to rapidly provide answers to clinicians' questions. We sought to determine clinicians' reasons for searching these resources, the rate of finding relevant information, and the perceived clinical impact of the information they retrieved. Methods: We asked general internists, family…

  18. A preliminary categorization of end-of-life electrical and electronic equipment as secondary metal resources.

    Science.gov (United States)

    Oguchi, Masahiro; Murakami, Shinsuke; Sakanakura, Hirofumi; Kida, Akiko; Kameya, Takashi

    2011-01-01

    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 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. PMID:21683566

  19. 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...

  20. 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.

  1. 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

  2. Theory of tunneling transport in periodic chains

    Science.gov (United States)

    Prodan, Emil; Car, Roberto

    2009-07-01

    This is a self-contained discussion of a recently proposed theoretical approach for off-resonance tunneling transport. The final result is an analytic formula for the asymptotic tunneling conductance involving the overlap of three well-defined physical quantities that can be easily evaluated with the standard electronic structure codes. We argue that the formula can be used to gain fresh insight into the tunneling transport characteristics of various systems. The formalism is applied to molecular devices consisting of planar phenyl chains connected to gold electrodes via amine linkers.

  3. Scanning Tunneling Microscope For Use In Vacuum

    Science.gov (United States)

    Abel, Phillip B.

    1993-01-01

    Scanning tunneling microscope with subangstrom resolution developed to study surface structures. Although instrument used in air, designed especially for use in vacuum. Scanning head is assembly of small, mostly rigid components made of low-outgassing materials. Includes coarse-positioning mechanical-translation stage, on which specimen mounted by use of standard mounting stub. Tunneling tip mounted on piezoelectric fine-positioning tube. Application of suitable voltages to electrodes on piezoelectric tube controls scan of tunneling tip across surface of specimen. Electronic subsystem generates scanning voltages and collects data.

  4. 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 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

  5. Gravitational Tunneling Radiation

    CERN Document Server

    Rabinowitz, M

    1999-01-01

    The isolated black hole radiation of both Hawking and Zel'dovich are idealized abstractions as there is always another body to distort the potential. This is considered with respect to both gravitational tunneling, and black hole "no-hair" theorems. The effects of a second body are to lower the gravitational barrier of a black hole and to give the barrier a finite rather than infinite width so tha a particle can escape by tunneling (as in field emission) or over the top of the lowered barrier (as in Schottky emission). Thus radiation may be emitted from black holes in a process differing from that of Hawking radiation, P SH, which has been undetected for over 24 years. The radiated power from a black hole derived here is PR e ^2__ PSH, where e ^2__ is he ransmission probability for radiation through the barrier. This is similar to electric field emission of electrons from a metal in that the emission can in principle be modulated and beamed. The temperature and entropy of black holes are reexamined. Miniscule...

  6. Ab initio description of tunnel junctions

    OpenAIRE

    Zahn, Peter; Mertig, Ingrid

    2000-01-01

    Based on spin-density functional theory we calculate the electronic structure of a tunnel junction consisting of two magnetic Fe layers separated by an insulating vacuum barrier selfconsistently. For the conductance the Landauer formula is evaluated in the ballistic limit as function of the magnetic configuration. Based on these conductances the tunnel magnetoresistance (TMR) ratio is obtained. We investigate the relation between TMR ratio and spin polarization of the electr...

  7. 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.

  8. Momentum Resolved tunneling in a Luttinger Liquid

    CERN Document Server

    Grigera, S A; Rabello, S J; Si, Q

    2003-01-01

    We consider momentum resolved tunneling between a Luttinger liquid and a two dimensional electron gas as a function of transverse magnetic field. We include the effects of an anomalous exponent and Zeeman splitting on both the Luttinger liquid and the two dimensional electron gas. We show that there are six dispersing features that should be observed in magneto-tunneling, in contrast with the four features that would be seen in a non-interacting one dimensional electron gas. The strength of these features varies with the anomalous exponent, being most pronounced when $\\gamma_\\rho=0$. We argue that this measurement provides an important experimental signature of spin-charge separation.

  9. Josephson tunnel junction microwave attenuator

    DEFF Research Database (Denmark)

    Koshelets, V. P.; Shitov, S. V.; Shchukin, A. V.; Baryshev, A. M.; Filippenko, L. V.; Fischer, Gerd Michael; Mygind, Jesper

    1993-01-01

    A new element for superconducting electronic circuitry-a variable attenuator-has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor-insulator-superconductor (SIS) Josephson tunnel junction when dc biased at different points in the current-voltage characteristic. Both numerical calculations based on the Tien-Gordon theory and 70-GHz microwave experiments have confirmed the wide dynamic range (more than...

  10. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... tendons, if those become swollen, that will put pressure on that nerve as it's crossing at the ... on in carpal tunnel syndrome, there is increased pressure in the carpal tunnel which causes some decreased ...

  11. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... pain, and potentially permanent numbness. To treat the condition, surgeons cut the carpal tunnel roof to decompress ... of what we do. There are multiple medical conditions that can be associated with carpal tunnel syndrome; ...

  12. Carpal Tunnel Release

    Medline Plus

    Full Text Available ... in the carpal tunnel is compressed, it can cause hand weakness, pain, and potentially permanent numbness. To ... off, there is a question: what are the causes of carpal tunnel syndrome? And I'm going ...

  13. 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 ...

  14. Dutch multifunctional motorway tunnel :

    OpenAIRE

    Van der Hoeven, F.D.

    2012-01-01

    The Landtunnel Utrecht at Leidsche Rijn has become a milestone in Dutch tunnelling because it signifies a remarkable leap forwards in the conceptualisation, awareness and insight into the use of underground space technology and tunnelling for environmental purposes. At the beginning of the 21st century, all motorway tunnels in the Netherlands (with the exception of the Schiphol road tunnel) were subsurface constructions that were built to pass waterways. The Landtunnel Utrecht at Leidsche Rij...

  15. Photonic tunneling times

    OpenAIRE

    Nimtz, G.; A. Enders; 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.

  16. Carpal Tunnel Surgery

    Medline Plus

    Full Text Available ... ligament. This is the ligament that forms the front of the carpal tunnel, and it’s the ligament ... back part of the tunnel, and in the front of the tunnel, it’s covered by this ligament, ...

  17. Resonant tunnelling through zero dimensional quantum dots

    International Nuclear Information System (INIS)

    When InAs is grown above GaAs or AlAs, a lattice mismatch between the two layers causes strain fields to develop. Above a critical thickness, these strain fields cause the InAs to form islands or dots. The dots are typically 10nm in diameter, and 4nm high. As the dimensions of the dots are below the typical electron wavelength, zero dimensional states are formed. In this thesis quantum dots are grown within an AlAs tunnel barrier. When a bias is applied between the top and bottom contacts of the device, resonant tunnelling is observed of electrons from the two dimensional electron gas formed in front of the AlAs tunnel barrier, through individual InAs quantum dots, despite the presence of several million dots within a typical sample. By measuring the tunnel current through a dot as a function of the applied bias, information can be gained as to the properties of the dot itself, and the electron gas from which tunnelling occurs. Conventional magneto-transport measurements are sensitive only to effects at the Fermi energy of the electron emitter gas. Due to the zero-dimensionality of the quantum dots, a single dot can be used as a spectroscopic probe of the occupied density of states of an electron gas at all energies between the Fermi energy and the subband edge, in a manner not available to any other measurement technique. Further, many body effects cause an enhancement of the tunnel current when the dot ground state is resonant with the Fermi energy of the two dimensional electron gas. The ground state of the quantum dot can also therefore be used to study many body processes at the Fermi level. (author)

  18. 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.

  19. 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

  20. Sequential tunneling and inelastic cotunneling in nanoparticle arrays

    OpenAIRE

    Tran, T. B.; Beloborodov, I. S.; Hu, Jingshi; Lin, X.M.; Rosenbaum, T.F.; Jaeger, H. M.

    2008-01-01

    We investigate transport in weakly-coupled metal nanoparticle arrays, focusing on the regime where tunneling is competing with strong single electron charging effects. This competition gives rise to an interplay between two types of charge transport. In sequential tunneling, transport is dominated by independent electron hops from a particle to its nearest neighbor along the current path. In inelastic cotunneling, transport is dominated by cooperative, multi-electron hops th...